remove-ai-watermarks/docs/module-internals.md

Module internals

This page documents the current implementation contract. It intentionally avoids experiment logs, corpus counts, and calibration history. Those records live in the verification plan and the research archive listed in the documentation index.

Read the relevant section before changing a subsystem. When this page and the code disagree, the code and its tests are authoritative and this page must be updated in the same change.

Architecture

The package has four main paths:

flowchart LR
    Input[Input file] --> Identify[Identify provenance]
    Input --> Visible[Visible mark removal]
    Input --> Invisible[Diffusion regeneration]
    Input --> Metadata[Metadata stripping]

    Identify --> Report[ProvenanceReport]
    Visible --> VisibleOutput[Localized and filled image]
    Invisible --> InvisibleOutput[Regenerated image]
    Metadata --> MetadataOutput[Container with AI metadata removed]

The all command runs visible removal, optional invisible regeneration, and metadata stripping in that order.

Command line interface

cli.py owns command parsing and user-facing exit behavior.

Important contracts:

• Single-image arguments reject directories.
• visible writes no output when no registered mark is selected and exits with EXIT_NO_VISIBLE_MARK.
• invisible writes no output when no supported local signal is found, unless --force is supplied.
• The two no-signal conditions currently share exit code 2.
• A quiet metadata --check and a successful metadata --remove (same for video metadata) end by repeating the identify limit: the pixel channel is untouched and a watermark such as SynthID has no local decoder once its metadata proxy is gone, so neither outcome is a clean verdict.
• Hard processing and write failures exit with code 1.
• all can still write the completed visible and metadata stages when the diffusion dependencies are unavailable, but exits with code 1 so the partial result is not reported as complete.
• batch counts per-file failures and exits nonzero if any file failed or an applicable invisible stage was skipped because its dependencies were absent.

The decorators for diffusion options are shared by invisible, all, and batch. The runtime help generated by Click is the source of truth for option names and defaults.

--adaptive-polish is tri-state: it declares default=None, so "the user did not choose" is a value the CLI passes through rather than a default it has to invent. resolve_adaptive_polish in watermark_profiles.py turns that None into the profile's answer (off for qwen-zimage, whose output already matches the input's detail level; on for sdxl-zimage). The same call runs inside InvisibleEngine.remove_watermark, so a library caller and a CLI caller on one profile get the same output.

It used to read Click's parameter source in the CLI instead. That put per-profile data in the argument-parsing layer, left the engine declaring the opposite default, and silently lost the polish for anything supplying the flag non-interactively (an envvar default or a wrapper calling main() with a defaulted list is classified DEFAULT). The seed follows the same rule: the CLI does not pre-resolve it either.

Regression coverage:

• test_cli.py
• test_cli_robustness.py
• test_optional_deps.py

High-level Python API

api.py provides the visible-mark entry points:

• remove_visible
• visible_provenance

and the image pipeline that the all and batch commands are thin wrappers over:

• remove_all, returning a RemoveAllResult after the visible, invisible, and metadata stages
• remove_batch, returning a BatchSummary for one directory and one mode
• InvisibleOptions, the invisible stage's knobs as one immutable value. Engine knobs only, under the engine's own names and defaults, so a bare InvisibleOptions() behaves exactly like calling the engine with no arguments. The engine takes them across two callables, __init__ for what shapes the loaded stack and remove_watermark for the per-image ones, so _run_invisible forwards each field to the right one rather than splatting the whole bag. Two defaults silently stopped mirroring: max_resolution=None reached _target_size's max_resolution > 0 and raised TypeError on every library call, and cpu_offload=True made a library run slower than the identical CLI run. TestInvisibleOptionsMirrorTheEngine compares the two signatures field by field, and deliberately keeps no exception table: a field needing one is a field that belongs elsewhere. force was such a field, and it decides whether the engine runs rather than how, so it is a parameter of remove_all and remove_batch next to backend and sensitivity
• MetadataStripIncomplete, raised before any write when AI metadata survives

remove_all reports progress as (stage, detail) pairs of stable tokens, not prose the caller has to parse back.

The package root exposes all of them lazily through __getattr__, keeping a plain package import free of the heavier image and model imports.

For path inputs, remove_visible reads provenance metadata, preserves alpha, and optionally writes and strips metadata. Array inputs are treated as BGR arrays and have no file provenance or separate alpha plane.

When no visible mark is removed, a same-format path copy preserves the original bytes. write_noop=False leaves the requested output path untouched instead.

Regression coverage:

• test_api.py
• test_image_io.py

video.py provides the high-level video entry point:

• identify_video
• inspect_video_metadata
• remove_video_all
• remove_video_batch
• remove_video_invisible
• remove_video_metadata
• remove_video_visible

The video API validates both the supported extension and container signature, then delegates all metadata detection and stripping to metadata.py. It requires a separate same-container output, defaulting to <source>_clean, so the product path does not overwrite an original. The package root exposes all functions lazily.

identify_video runs the same stable-mark selection helper as remove_video_visible, so a provenance report cannot authorize a mark that the removal path would reject. It reports an empty local result as unknown rather than clean. Identification skips the separate per-frame timestamp probe because it never encodes frames. remove_video_all is the predictable-output composition: visible removal plus verified metadata stripping by default, with a same-container passthrough when neither signal exists. The lossy invisible removal stage is an explicit opt-in through the oracle-certified profile. remove_video_batch applies those contracts sequentially across a top-level directory, returns every per-file failure, and byte-copies visible no-ops so a successful output set has no silent holes. An invisible batch loads one VAE runtime and reuses it across every compatible file; a failed model load is reported per file without retrying the same multi-GB initialization.

Native MP4/MOV TC260 labels follow TC260-PG-20257A: moov.udta.meta.keys maps an AIGC key to a raw JSON value in ilst. _internal/isobmff.py walks those nested boxes by seeking, so detection reaches a tail moov without reading the preceding mdat. Two Doubao iOS variants sit outside that normative placement and are covered by the same walker (2026-08-17 corpus findings, both previously undetected): a QuickTime-form meta box as a direct moov child (no FullBox header, disambiguated by probing the child-box offset), and a QuickTime hdlr=mdir metadata list under udta.meta whose ilst data items carry the validated JSON with no keys box at all (content-validated, so only genuine TC260 JSON matches; the keyless entry has no key name to blank, so its value alone is spaced out). The MP4/MOV/M4V/M4A removal path first validates the top-level box walk, then copies the source to a sibling temporary file in bounded chunks. Supported C2PA/JUMBF/AI-label boxes become same-size free boxes with blank payloads; TC260 removal changes the four-byte key to free and blanks only the validated JSON value with same-length spaces. This preserves every box size, stco/co64 offset, encoded stream byte, and source-sized memory bound. Publication is atomic, and a malformed top-level walk is copied unchanged. A generic AIGC key whose value has no TC260 field is ignored.

_internal/ebml.py provides the corresponding bounded Matroska/WebM reader. It seeks over clusters and accepts only a Segment.Tags.Tag.SimpleTag pairing TagName=AIGC with a JSON TagString carrying a TC260 field. The existing ffmpeg stream-copy path removes those container tags without transcoding the encoded streams.

_internal/riff.py and _internal/flv.py implement the remaining normative TC260 video placements. The RIFF walker reads only AVI LIST/INFO/AIGC children. The FLV walker skips media tags and parses the AMF0 script.onMetaData.AIGC string. Both require a recognized TC260 JSON field and use the verified ffmpeg stream-copy path for removal.

video_encoding.py owns the ffmpeg command and pipe lifecycle shared by visible removal and invisible regeneration. It centralizes container codecs, optional audio stream copying, metadata/chapter policy, encode-failure reporting, and atomic same-directory publication. Each mapped stream is allowed to reach its own end, so a copied audio tail is not shortened to the frame-input duration. Both the raw-BGR and timestamped-NUT stdin modes redirect ffmpeg stderr to a temporary file while frames are written. Waiting to read diagnostics until after stdin closed allowed stderr backpressure to stop ffmpeg's frame reads, which in turn blocked the producer before it could close stdin. The file consumes no pipe capacity or RAM while ffmpeg runs; completion reports a bounded head and tail when diagnostics are unusually large. Aborts release it even when ffmpeg has already exited. A real subprocess regression writes diagnostics beyond pipe capacity while streaming frames, checks bounded failure reporting, and the Linux full-clip CI job guards the complete path. Frame encoding and source-audio copying run as two ffmpeg processes in sequence. The streaming encoder has only the frame pipe as input, so input probing or demux queues cannot deadlock the producer against a second input. After that pipe reaches EOF, a finite stream-copy mux combines the encoded video with the source audio and applies the requested metadata/chapter policy. Both stages use sibling temporary files, and only the completed mux is published atomically. The mux also redirects diagnostics to disk and reports only a bounded head and tail. Command regressions assert the single-input encoder and final map targets; failure regressions cover bounded mux diagnostics and atomic cleanup. probe_video_encode_profile reads the first source video stream with ffprobe and preserves the supported properties that survive the 8-bit BGR boundary: yuv420p/yuv422p/yuv444p chroma sampling, recognized color tags, encoder time base, MP4/MOV track timescale, source pixel format, and component depth. Both raw-CFR and timestamped-NUT inputs use ffmpeg's passthrough FPS mode. This keeps one encoded frame per supplied frame when an older ffmpeg receives a fine-grained source encoder time base such as 1/90000; implicit synchronization can otherwise synthesize thousands of duplicate frames between CFR timestamps. HDR transfer functions and component depths above 8 bits are rejected before encoding so the OpenCV boundary cannot silently reduce them to SDR 8-bit. probe_video_timestamps reads authoritative per-frame display PTS through ffprobe. OpenCV timestamps are only a count-matched fallback when ffprobe is unavailable or fails; this avoids decoder anomalies such as one spurious negative first-frame timestamp turning a CFR clip into false VFR. A uniform sequence keeps the cheap raw-BGR pipe unless the source starts at a non-zero PTS. A variable or offset sequence is packetized by the lazy PyAV bridge as rawvideo in an in-memory NUT stream with explicit PTS. System ffmpeg reads that stream with -fps_mode passthrough; -copyts additionally retains a non-zero video start and the corresponding copied-audio offset. No temporary frame sequence or second video encoder is introduced.

video_temporal.py owns the shared optical-flow maps and temporal residual metric. Visible removal uses stabilize_filled_frame after the selected image backend: it works on a bounded crop around adjacent masks, backward-warps the prior cleaned frame, requires high warped-mask coverage, and gates blending on an unmasked source-context ring. Only covered current-mask pixels change. Scene cuts, disjoint marks, and poor motion matches therefore retain the independent current-frame fill. The same module supplies the motion-compensated metric used by the invisible-video sweep.

video_invisible.py implements the oracle-certified video SynthID removal engine. It samples frames uniformly, resizes to a VAE-aligned geometry, encodes each frame to latent space, applies one seeded spatial-noise field across the entire sequence, and decodes fresh pixels. Reusing a single noise field avoids independent frame-to-frame noise. The shipped path retains only one configured frame batch, updates PSNR and temporal residuals incrementally, and streams BGR frames directly to the video-only ffmpeg encoder. A separate stream-copy mux then adds optional source audio and drops all source metadata. The result is written through same-directory temporary files and atomically replaced only after both stages succeed.

The engine returns PSNR and a motion-compensated temporal-residual ratio as quality measurements. Neither is a watermark detector. The high-level result reports completed removal without a separate verification-status flag. The companion scripts/video_synthid_sweep.py imports the same engine helpers to build a matched control and candidate grid, preventing research and shipped regeneration paths from drifting.

The engine's psnr_db is measured against the already-resized frame and before the encoder, so it scores the VAE round trip plus latent noise and cannot see the downscale, the decimation, or the codec. No in-loop metric can: the candidate frame is captured before it reaches the encoder pipe. scripts/video_fidelity_probe.py covers the rest by decoding the delivered file after muxing, upscaling it back to the source geometry, and scoring it against the untouched source frames. It also reports the delivered file's bitrate, so a fixed-crf bitrate rise cannot read as unchanged quality; because the mux copies source audio verbatim, that figure is a container bitrate, not a video one. The probe streams and accumulates the same way the engine does, so its peak memory does not grow with clip length. It drives the source through the engine's own _iter_sampled_frames at the source geometry rather than repeating the selection rule: a frame-count check cannot catch a rule that reorders frames without changing how many, so the rule itself has to be shared.

load_video_vae_runtime asserts the default model's latent scaling factor against VIDEO_SYNTHID_VAE_SCALING_FACTOR and warns that no certified profile exists for any other model. The published sd-vae-ft-mse config carries no scaling_factor key, so the value is a diffusers class default under an upper-unbounded pin, and the certified profile is a perturbation-to-signal ratio rather than a bare noise_std. A library bump that moved that default would otherwise rescale every perturbation with a green suite. The validated factor is carried on VideoVaeRuntime and passed into encode and decode, so the gated value and the applied value are one measurement rather than three independent reads. scripts/video_synthid_sweep.py loads through the same function: the harness that produces the certified rows is the last place that should be exempt from the gate. The full-clip oracle floor is noise_std=0.15: on the public eight-second Veo carrier, 0.10 remained detected while 0.15 did not.

video_visible.py implements the first pixel stages for Sora, Veo, Seedance, Dola, Hailuo AI, and Kling AI. The Sora detector searches a normalized frame with a fully synthetic mascot-and-text silhouette at several scales. The Veo detector uses separate synthetic silhouettes for the current four-point diamond and legacy Veo text. Seedance uses a synthetic rounded boxed-AI silhouette, while Dola uses an OpenCV-font Dola AI silhouette. Hailuo AI uses a synthetic waveform, MINIMAX/Hailuo AI text, separator, and ring. Kling AI combines synthetic font variants with a ring approximation of its swirl; the logo path rescues wordmarks whose version or font differs, while the edge and white-label gates reject recurring scene texture. All fixed-mark searches are bounded to the expected lower-frame area and calibrated independently. A strong relocated Veo diamond may bypass the known layout anchors, but weak free-corner matches never enter the temporal arbiter.

The default auto route decodes each frame once, shares its grayscale and normalized representations across all detectors, and caches resized synthetic template features for the fixed stream geometry. Provider confidence scales are not comparable: selection applies each provider's temporal arbiter and takes the first stable result in specificity order (sora, veo, seedance, dola, hailuo, kling). An explicit mark uses the same scan path with one candidate. Removal also collects authoritative per-frame timestamps for the encoder, while identification omits that unused ffprobe pass.

Every per-frame result is untrusted. Each provider's floors, minimum-run policy, fill padding and mask style are one row in VISIBLE_MARK_POLICIES, and every mark enters the same stabilize_localizations entry point; the recurrence implementation underneath knows nothing about providers. That policy row also carries accepts_provenance, which forces provenance=False for Hailuo AI and Kling AI — they have no metadata that could confirm them, and the guarantee used to be structural (their wrappers took no provenance parameter at all). Provenance can relax a low-contrast run only after recurring visual evidence exists. Sora transition frames follow the nearest confirmed moving position only with Sora provenance. Seedance, Dola, Hailuo AI, and Kling AI additionally require candidates to remain anchored to the start of a run. This rejects slowly drifting scene details that still have high frame-to-frame overlap. Hailuo AI and Kling AI do not infer provenance from technical encoder tags; their confirmed public samples carried no provider metadata.

Removal runs in a second decode pass. Sora, legacy Veo text, Dola text, Seedance, Hailuo AI, and Kling AI use box masks. Seedance deliberately fills the complete localized box: a synthetic outline mask passed repeat detection but left part of the real translucent border visible during visual end-to-end review. Hailuo AI expands beyond the matched core to cover both provider icons. Kling AI expands around the wordmark or swirl to include the version and optional PRO suffix. The square Veo diamond uses a synthetic shape mask so transparent corners do not erase unrelated pixels. Every mask goes through the shared watermark_registry.fill backends. ffmpeg encodes the changed video stream and copies optional audio. The default OpenCV fill is the speed floor; structured backgrounds need MI-GAN or LaMa for better reconstruction. Invisible video stages must continue to reuse the image and metadata implementations rather than copying their logic.

Regression coverage:

• test_video.py, including a real ffmpeg full-clip Sora/OpenCV path that generates a synthetic marked MP4 with AAC audio and C2PA provenance, runs both remove_video_visible and the composed remove_video_all API without mocks, and verifies complete removal, frame count, frame rate, duration, untouched-region PSNR, paired temporal deltas inside the filled region, byte-identical copied audio packets, source stream properties, metadata stripping, and a large-mdat metadata case that rejects any full-source read_bytes() call. CI installs ffmpeg explicitly for this test so the integration gate cannot silently skip.
• test_video_fidelity_probe.py, which builds its clips from solid-color frames whose index is recoverable from the pixels, so a decimation that keeps the frame count but shifts the phase scores far worse instead of passing unnoticed. It also asserts that the probe binds the engine's sampler rather than a copy of it, and it holds the suite's only constraint on that sampler's phase. Nothing here needs a model, but it does need ffmpeg, so CI runs this file in the same job that installs it.

Metadata and provenance

C2PA

_internal/c2pa.py reads C2PA with the official c2pa-python reader first. Its byte-level PNG parser remains a fallback for partial and synthetic fixtures that the official reader rejects.

Structured extraction is limited to the active manifest and the ingredient manifests reachable from it. Validation is preserved as separate dimensions: asset binding integrity, claim signature, signer trust, and signer certificate validity. A matching asset hash and valid claim signature do not make an untrusted or expired signer trusted, so those stay separate fields and separate caveats -- but they do not lower confidence. identify assigns high confidence when the asset binding and the claim signature both validate, medium confidence to a claim that validated nothing (fallback parsing, unknown dimensions), and no origin verdict to a binding failure, a signature failure, or a revoked signing credential. The failed claim remains in the marker inventory and keeps the removal gate fail-safe because a post-signing container edit can invalidate C2PA without removing a declared pixel watermark.

Revocation reaches the disqualifying branch through signer_validity, not through binding or signature. A check that read only the latter two returned a confident AI verdict off a credential the issuer had disowned, with an empty integrity_clashes -- quieter than a hash mismatch on the same file. Certificate expiry is deliberately not disqualifying: an expired certificate does not imply the signed bytes changed, and a signature actually made outside validity already arrives as claimSignature.outsideValidity.

One rule, one place. _validation_fields maps status codes to the four dimensions and also emits c2pa_failed_codes, the subset of failures that actually drove a dimension to invalid; c2pa_info_has_invalid_credential maps those dimensions to disqualified, and both the ingredient-reachability walk and the report consume that single path. The displayed reason comes from c2pa_failed_codes rather than a substring rescan of the full code list, so what a caller is shown as the cause cannot become a looser rule than the verdict it explains.

The structured walk also treats an exact known AI product in a reachable claim_generator as an AI assertion. This covers update chains where the active manifest names only c2pa-tool while a validated ingredient names Dreamina, and Firefly chains that identify Adobe_Firefly without repeating a digital source type. Unreachable manifests remain excluded.

Reachable c2pa.soft-binding* assertions retain their exact alg and bounded, printable block value in addition to the normalized vendor label. A block value without its algorithm is not surfaced because it cannot be attributed to a decoder or registry entry. com.microsoft.invismark.1 uses that value as the pixel-watermark identifier in Microsoft Paint output. An InvisMark soft binding keeps the invisible-removal gate fail-safe even when the C2PA asset binding has since become invalid, because metadata damage does not prove the pixel carrier disappeared. identify retains the generic soft_binding signal for schema-1 compatibility and adds invismark as the stable pixel-removal signal. Content-fingerprint soft bindings do not trigger pixel regeneration.

The SDK default enables trust verification but supplies no production trust anchors. Consequently, an installation without an explicitly maintained C2PA trust bundle reports every otherwise valid signer chain as untrusted -- signingCredential.trusted appears in no default installation, from any vendor. Confidence therefore must not depend on it. It did from 0.27.0 through 0.30.0, which made the high-confidence branch unreachable in production while a hand-built fixture stamping signingCredential.trusted kept it green in the suite; measured on the committed provenance fixtures, every C2PA file from OpenAI, Adobe and Black Forest Labs came back untrusted, and an intact manifest scored the same medium as a fallback parse that validated nothing. That collapsed the one distinction the official reader exists to draw. tests/test_identify.py::TestIdentifyRealSamples::test_no_committed_fixture_reports_a_trusted_signer is the reachability guard: it asserts the fixtures really are untrusted and still reach high confidence.

Read untrusted here as a missing input, not a finding: nothing was checked, because there was nothing to check against. If a maintained trust bundle is ever configured, that stops being true and the confidence mapping in _c2pa_credential_level must be re-read, because only then does a failed trust check mean the signer was rejected. Shipping or fetching an official trust bundle requires a separate update, provenance, and availability policy; do not silently convert signingCredential.untrusted into trusted based on a vendor-name match.

Vendor attribution comes from the registry in _internal/constants.py. Derived issuer and platform maps should not be maintained separately. For an AI C2PA claim, a recognized product in claim_generator takes precedence over the certificate issuer: an application can sign through an upstream model provider without becoming that provider's product. Only exact product mappings receive this precedence; an unknown claim generator still falls back to issuer attribution. An unmapped issuer org reads as unknown-signer C2PA with no platform; that is how Ideogram was surfaced (4 corpus uploads signed "Ideogram, Inc", 2026-08-08) before its vendor row was added on 2026-08-27.

Metadata scanning and stripping

metadata.py contains the shared metadata scanners and remove_ai_metadata.

Key contracts:

• scan_head is the shared cached input for bounded byte scans. It fills the buffer in two layers. Structural readers first, one per container, each seeking past the pixel payload to reach metadata placed beyond the window: isobmff.scan_c2pa_region, _png_late_metadata, _riff_late_metadata. A decoder-backed fallback last, _decoder_visible_text, for metadata the raw bytes do not spell at all — a zlib-compressed PNG zTXt packet is readable only after inflation. The layers are ordered that way because the structural readers work on files no decoder can open.
• A C2PA reader failure is logged at warning, not debug. It returns the same None as a file with no manifest, so nothing downstream can distinguish "no credentials" from "the credentials could not be read", and the second silently downgrades a verdict.
• JPEG stripping walks metadata segments and preserves the entropy-coded image scan.
• Exact app-export JSON disclosures in EXIF ImageDescription or UserComment share one parser. Known AI-product provenance is removable without by itself asserting that the pixels were generated; explicit aigc_info discriminator values and Dreamina exportType=generation do assert AI origin. Ordinary Aweme, retouch, and lv editor exports are preserved.
• ISOBMFF containers use _internal/isobmff.py.
• Native MP4/MOV TC260 AIGC entries are read from moov.udta.meta.keys/ilst and blanked without changing box sizes.
• Native MKV/WebM TC260 AIGC entries are read from Segment.Tags.Tag.SimpleTag and removed through the ffmpeg stream-copy path.
• Native AVI and FLV TC260 entries are read from LIST/INFO/AIGC and script.onMetaData.AIGC, respectively, then removed through ffmpeg stream copying.
• Supported non-ISOBMFF audio and video containers use ffmpeg stream copying.
• The low-level remover is fail-safe and can copy an undecodable file through unchanged.
• A caller that reports success must use strip_and_verify, which scans the written output for surviving markers. If the metadata-preserving decoder rejected the container but image_io can still decode its raster, strip_and_verify normalizes that raster and scans again. A truly undecodable file keeps the surviving-marker result.

Detection and removal must stay in parity. A new marker is incomplete until the scanner can find it, the remover can reach every supported placement, and a test proves that it no longer appears in the output.

Regression coverage:

• test_metadata.py
• test_metadata_internals.py
• test_security_clamp.py

Provenance report

identify.py separates file-backed metadata extraction from verdict logic:

• extract_provenance_evidence reads the supported metadata signals into ProvenanceEvidence.
• evidence_from_metadata_record normalizes an externally collected nested metadata record into the same evidence type without file access. Versioned native records accept only source-derived fields; filenames, hashes, timings, errors, prior verdicts, and pixel results cannot become evidence. Unknown native schema versions and other record types are rejected.
• The vendor registries are matched over _metadata_region(head), not the whole scan buffer: they see the container's metadata and not its coded pixels. The tokens are raw substrings and the shortest are four and five bytes, so over a megabyte of compressed data one turns up by chance, and the entry it hits may assert AI. The trim happens only when the container parses -- a malformed or unknown one is left whole, because dropping real evidence to avoid a chance match is the wrong trade.
• identify_from_evidence evaluates that evidence without reopening the source. Rules that decide a verdict live here, not in extraction: extraction has two implementations, and a rule in only one of them is a rule the other lacks. The SynthID provenance evidence is the worked example — its structured form comes from the manifest, and the byte-scan fallback for containers no parser reaches runs in the verdict, so both extractors reach the same answer. It did not, and the record path silently reported no SynthID for images the file path flagged.
• identify preserves the path-based API and adds the optional registered visible-mark and open invisible-watermark detectors after extraction.

SynthID periodic carrier detector (research only)

The local lattice expert is not part of the public package. Runtime code lives in scripts/synthid_runtime/ and the campaign log is synthid-detector-research.md. The notes below are the calibration history of that research expert.

synthid_detector.py is the runtime form of the frozen 2048x2048 periodic-tile experiment. It folds a Gaussian high-pass residual modulo 16x16 within a calibrated pixel-count range and compares the normalized RGB tile with the bundled float64 template scripts/synthid_runtime/synthid_periodic_tile_2048_v1.npz. Exact multiples use the original reshape-and-mean path; other sizes use count-correct modulo folding, without resize. Channels are filtered and folded sequentially, and partial edge blocks are accumulated without a full-frame padding buffer so the 18-megapixel ceiling does not require multiple three-channel float workspaces. The model hash is pinned by a test, and the unchanged operating threshold is 0.17357069773071196 through 10 megapixels.

That fixed threshold is not production-qualified. A later source-fresh Open Images test-split challenge produced 5 crossings among the 211 images in its supported geometry. A precision-first 0.28 replacement is frozen as a research candidate after retaining all 12 available source-diverse native positives and rejecting those five crossings. It then failed the second untouched holdout at 1/213, with score 0.322542963. The replacement is rejected and fixed-v2 remains an explicit diagnostic only.

The direct API returns detected, indeterminate, or unsupported. Passing register_scale=False selects fixed-v2 from 1,000,000 through 10,000,000 decoded pixels as an explicit diagnostic. Its frozen threshold accepted none of 5,000 public COCO views balanced across every observed target geometry, and none of a separate 5,000-view challenge over 256 generated geometries covering every pair of modulo-16 edge remainders. The original 2048x2048 verdicts and exact scores remain unchanged. Runtime matches do not attribute a provider. identify adds only positive matches as high-confidence evidence and never turns a local negative into a clean verdict. The result envelope also names the signal family, provider scope, backend, whether metadata contributed to the verdict, whether pixels were preserved, and an explicit reason for unsupported or indeterminate results. These fields are shared with the official OpenAI verifier's JSON boundary.

The production router selects synthid-periodic-tile-large-v1 above 10 through 18 megapixels when both dimensions are at least 2,048 pixels. It evaluates all phase-aligned 2,048-square windows and combines the minimum fixed-template, Red-minus-Green, and Blue-minus-Yellow spatial correlations with the most negative Blue-minus-Yellow mid-band correlation. The 3072x5504 portrait geometry also applies a Green mid-band alias veto. Each component is normalized to its frozen gate and the public threshold is 1.0.

All 37 inferred large candidates cross the rule, and all seven metadata-free, pixel-identical candidates checked by the official Gemini verifier were detected. The constants rejected all 17,417 exposed external controls. A post-freeze production-path challenge then rejected all 2,637 decoded-pixel- unique controls drawn from 2,000 COCO images excluded from the earlier large color-phase challenge and 637 deduplicated Picsum controls. Four large geometries and four resampling kernels were balanced; the maximum score was 0.0592777965. The source collections were not freshly acquired, so this is a feature-unseen holdout rather than a fresh-source estimate.

A separate post-freeze Open Images download yielded 41 completed, decoded-pixel-unique controls after excluding incomplete .aria2 files and all prior Open Images hashes. The frozen production path accepted 0/41 and reached a maximum score of 0.4083013324. This source-fresh audit is too small to replace the main holdout interval but checks the acquisition boundary.

The same seven official positives were then re-encoded at unchanged dimensions. JPEG-95 and JPEG-90 each reduced detection from 7/7 native files to 0/7. The large operating point is therefore native-pixel and lossless-copy support, not a codec-robust claim.

Arbitrary geometry is not the same as arbitrary spatial resampling. On a stratified 80-image fixed-positive sample, one-step resizes at seven nonidentity scales from 0.5 through 1.5 reduced the unchanged 16x16 detector from 80 accepted sources to zero at every scale. Restoring the original geometry recovered 58-80 sources, showing that the carrier period scaled with the pixels. A discovery bank that scaled the template to integer periods 8, 10, 12, 14, 18, 20, and 24 was promising: a threshold frozen above 3,000 resized COCO controls accepted no view in a 2,000-control final partition and accepted 672 of 800 source-disjoint provider positives. It also stayed below threshold on the tracked OpenAI and Adobe controls. The branch remains research-only because noninteger periods at scales 0.8, 0.9, 1.1, 1.2, and 1.333 collapsed, while separate per-period thresholds accepted five final controls. The runtime therefore keeps only the fixed 16-pixel lattice.

A follow-up fractional-period probe sampled the 30 strongest template harmonics over a continuous 7.5-24.5 period range. The correct period appeared within 0.05 pixels among the top three candidates for 58 of 60 transformed positives. Testing nine neighboring reconstructed geometries then recovered 44 of 60 at the native threshold, compared with an upper bound of 48 when the true source geometry was supplied. The complete search still failed its small frozen control split: a threshold above 250 development controls accepted two of 150 final controls. Multiplying the canonical score by spectral-period confidence also accepted two. That baseline was rejected rather than shipped at its discovery threshold.

The research-only synthid_affine_lattice_probe.py adds split-confirm synchronization. It estimates complex harmonic coherence on one checkerboard of patches, confirms the selected period on the other, and reports amplitude-aware confirmation, a locally content-whitened multichannel code match, and phase-preserving and cyclically registered template scores. A 0.1-pixel grid recovered the expected 12.8, 14.4, 17.6, and 19.2 periods in 20/20 transformed views from five official positive parents. A provisional conjunction accepted none of 800 corresponding views from 200 oracle-negative parents, none of 469 OpenAI-labeled rows, and three of 276 broad non-Google rows whose TC260 or Samsung provenance prevents treating them as clean oracle negatives. This probe is not runtime routing: positive diversity is still inadequate, period 8 remains rejected, and the amplitude stage currently handles isotropic scale at zero rotation only. Full protocol and caveats are in the detector research plan.

The whitened match uses neighboring noncarrier bins to estimate complex Green/opponent-color covariance around every selected harmonic. It corrected a period-24 alias on one native official positive, giving the broad native search the correct period 16 on all five ordinary-size positives. It was retained only as a candidate reranker: its positive-to-negative margin was smaller than the existing spatial-template margin in both the native pilot and a locked 0.8 resize challenge. Two of the three TC260/Samsung-provenance challenge crossings also matched the full whitened code more strongly than the weakest official large positive, so the pixel result identifies a compatible signal family, not a provider.

The same probe also exposes a payload-agnostic H5 confirmation. It estimates a complex harmonic vector independently on the two checkerboards and measures their fixed relative-phase inner product; the codeword need not match the known template. Free cyclic-shift selection was rejected because natural phase aliases overlapped the controls. The fixed all-harmonic statistic separated five native official positives from 130 controls with margin 0.1619, and five 0.8-resized views from 200 fresh-parent controls with margin 0.1541; all seven large official positives also passed the observed gap. It remains research-only because these tests supplied the period, reuse one negative source family, and contain only 12 independent positive parents.

The separate research-only synthid_cyclostationary_probe.py measures full complex cross-channel spectral correlation at carrier shifts against neighboring-shift same-image nulls. It recognizes synthetic amplitude modulation and rejects both independent noise and a purely additive carrier. The real native pilot overlapped completely: five official-positive joint contrasts ranged from -0.0027 to 0.0337, while 130 controls reached 0.0593. The cyclostationary branch is rejected rather than tuned on new frequency bands.

The affine-lattice research CLI also supports symmetric in-memory JPEG and top-left crop challenges. At fixed native period 16, codec-specific phase-preserving template thresholds retained all five repeated positive views and accepted none of 80 locked controls at JPEG qualities 95, 90, and 80. The locked margins declined from 0.1054 to 0.0257; whitened and unknown-codeword scores were rejected for lossy JPEG. A separate registered crop conjunction retained all five views and accepted none of 80 controls after both 5% and 10% top-left crops, with registered-template margins above 0.22. These are research pilots, not runtime experts: the period was supplied, positive parents were reused, and only one codec implementation and one negative family were tested.

The register_scale=True path is the calibrated ordinary-size production expert. It keeps the harmonic search, adds three-level scale-space consistency and quadrant agreement. Its calibrated decision requires the canonical winner to be the strongest spectral-period candidate, its three-way amplitude to cross the threshold for that period bin, and both independent high-frequency template bands to correlate by at least 0.075. The public registered score is the minimum normalized margin across those gates, so its decision threshold is 1.0.

The earlier single-threshold version produced 68 false positives among 11,273 symmetrically downscaled Spaces controls. A top-candidate plus period-bin version removed those but still produced 6 false positives among 1,000 source-independent Open Images controls. The high-band gate removed them and then accepted none of 499 previously untouched Open Images reserve controls. The resulting rule retained 229 of 355 source-disjoint transformed positives: 0/65 at scale 0.5 and 229/290 from scale 0.65 through 1.5. The explicit period-8 rescue is rejected because resize lattices fully overlap its positive distribution.

A subsequently frozen 1,000-image Open Images reserve accepted zero in registered mode. The fixed expert supported only 81 of those geometries and accepted seven, so fixed and registered results cannot safely be unioned. In overlapping geometry the registered decision remains the validated path; fixed-only evidence is a diagnostic rather than a universal-cascade positive.

A later source-fresh 3,000-image Open Images test-split challenge superseded the registered-v2 precision claim: it accepted 4 of 2,997 supported controls. The registered-v3 confirmation uses disjoint patch groups for phase, cyclic amplitude, and held-out-codeword evidence. It rejected all four crossings, retained 147 of 148 base-accepted source-diverse positives, and retained all 359 base-accepted views in a dense 0.65-1.50 transform matrix over 12 independent parents. Frozen unchanged, it then accepted 0/2,996 controls from a second nonoverlapping Open Images cohort and 0/2,366 supported controls from a 3,000-image COCO second-family challenge. Registered-v3 is now the default ordinary-size positive route. The exact gates, acquisition hashes, and rejected weak-signal rescue are recorded in the detector research plan.

Every one of those control rates is photographic. Against 223 corpus images whose C2PA names a non-Google generator, the unchanged entry point accepted 29 (0.130, Adobe Firefly 0.241, highest foreign score 3.01), all from registered-v3. The branch reads a lattice shared across generation pipelines, which is why it must not be reported as a watermark. The public identify path no longer calls this expert.

The branch is also phase-locked to the image origin, exactly like the large expert. A two-pixel diagonal crop killed all 28 in-geometry foreign detections and all 8 detected Google provenance positives (maximum remaining scores 0.779 and 0.311 against the 1.0 threshold); the signal recovers only at offsets that are multiples of four. Registered-v3 therefore detects the same crop-destroyed generation-pipeline lattice as large-v1, on ordinary sizes.

When registered-v3 abstains, opponent-registered-v1 searches the same frozen template in Red-minus-Green and Blue-minus-Yellow space. It reranks three separated scale candidates with fixed RGB and two spatial opponent-color gates, then accepts only periods 7.9-12.0 on 1-10 megapixel rasters whose sides are at least 768 pixels. Period-8 candidates additionally require Red-Green and Blue-Yellow 8-pixel edge ratios no greater than 1.05; this vetoes the deterministic JPEG block lattice without using container metadata. The final rule recovered 49/49 lossless 0.5x-0.75x views from seven official-positive parents. It rejected all 1,790 measured period-8 codec crossings, while 350 identically resized controls had no base crossing and the earlier period-band rule accepted 0/1,000 post-freeze Picsum controls. Period 12.8 remains excluded, and lossy JPEG/WebP views remain inconclusive.

The runtime precedence is registered-v3, the bounded opponent fallback, then large-v1 above 10 megapixels. Passing register_scale=False selects the legacy fixed diagnostic explicitly. The research bank in scripts/synthid_routed_expert_bank.py keeps all three observations for audits. Neither runtime nor research routing returns a clean-image verdict.

An unchanged registered challenge from 10 to 18 megapixels retained only 1 of 37 Google candidates and zero of 89 non-Google controls. Twenty-eight positives cleared amplitude, 21 had matching spatial and spectral periods, but only three cleared high-band agreement. The 10-megapixel ceiling therefore remains. Phase-aligned 2,048-square fixed windows did not provide a fallback: median consensus retained 36 positives and accepted 10 controls, while all-window consensus retained 36 and accepted eight. One frozen full-frame pre-resize to eight megapixels also retained only the same 1 of 37 positives and zero controls; just three positives cleared high-band agreement. Large images therefore cannot be routed through a canonical-size registered fallback; the later native opponent-color branch is separate. The remaining phase-aligned window variants closed this branch: a single center 2,048-square registered window retained 1 of 37 positives and zero of 89 controls, while accepting any phase-aligned 2,048-square window retained 2 of 37 and zero controls. The latter control maximum was already 0.968 against the 1.0 decision threshold. Neither the coverage nor the exposed specificity margin supports a registered-window expert; these results do not apply to the later native opponent-color branch.

A separate half-scale patch-consensus branch initially looked promising. Its 64-pixel, 90th-percentile patch statistic retained 33 of 49 validation positives and zero of 166 controls, then 27 of 52 locked-test positives and zero of 140 controls. The frozen broad challenge rejected it: 61 of 10,906 symmetrically half-scaled Spaces controls and 22 of 1,000 independent Open Images controls crossed the unchanged threshold. A post-challenge Green negative-phase spread gate removed those errors but retained only 2 of 234 later Google rows and zero of 689 later controls. Half-scale support therefore remains explicitly absent.

An independent reproduction of the public aloshdenny/reverse-SynthID V4 cross-color codebook did not provide another expert. Its best-of-two-model phase rule retained 141 of 355 positives but accepted 191 of 499 controls and 386 of a fresh 1,000-control reserve; AUC was 0.517. The repository's stricter aspect-ratio routing reduced coverage but preserved the same approximately 38% positive and control acceptance within supported rows. Its older V3 phase score had AUC 0.473, and two prespecified amplitude-aware V4 rerankings reached only 0.521 and 0.524 AUC. These external rules are research baselines only. Their useful contribution is the solid-reference phase-consensus construction, not either published single-image threshold. Full methodology and the DALL-E reference-set confound are recorded in the detector research plan. A later exact repeat on the hash-disjoint v7 challenge confirmed the same failure: the published cut accepted 77/200 Google and 76/200 OpenAI, so it did not separate the two target providers. A direct exact-1024 reproduction of the same V4 artifact confirmed rather than rescued that verdict: the union of its two published profiles accepted 177 of 443 Google rows and 60 of 162 controls. The artifact's floor left only about two active bins in the inspected profile/channel, explaining why its score acts as a weak generic phase-coherence test rather than a specific codebook match.

An exact-1086x1448 OpenAI follow-up also rejected the solid-reference transfer. A low-texture 256-bin phase codebook achieved native and JPEG-95 test AUCs of 0.512, and independent train halves shared only two exact bins. The paper's content-dependent alternative was tested with 60 OKLab masking-alignment features. Its native/JPEG minimum reached test AUC 0.593 and 15/562 positives versus 1/228 controls at the frozen boundary, but deterministic half-fits shared no positive decision and had coefficient cosine 0.148. Neither branch is a runtime OpenAI expert.

An exact-1254 assertion-contrast search selected an sRGB period-8 Blue-channel direction at 45 of 259 validation asserted rows and zero of 16 same- or other-provider validation rows. It failed its locked specificity check at 39 of 233 asserted rows and one of 18 controls. Across the complete exact-geometry audit it accepted 185 of 992 asserted rows, one of 55 same-provider rows without an assertion, and one of 13 other-provider rows. Raising the threshold above the wider controls reduced recall to a small minority, so this branch remains research-only.

Three attempted veto or missing-codeword rescues also failed. The official InvisMark decoder checkpoint passed its own embedded-watermark self-test at 0.997 confidence and 0.97 bit accuracy, but all OpenAI and provider-control cohorts clustered around 0.18 confidence with no useful separation. DTCWT modulus before periodic folding retained 5 of 158 locked-test OpenAI rows and zero of 135 controls, then zero of 40 fresh OpenAI rows. A 16-codeword whitened period-8 model retained 5 of 158 and zero controls, then 1 of 40 fresh OpenAI rows and 1 of 50 fresh controls. They neither explain the known oracle-positive miss nor justify runtime routing.

An image-level patch-bag model over nine normalized high-pass patches was the strongest later local OpenAI classifier. It accepted 324/1,364 development-test OpenAI rows with 4/3,373 heterogeneous controls, then transferred to 120/486 OpenAI rows, 8/504 general controls, and 5/33 same-provider non-assertion rows in the later temporal challenge. Assertion enrichment over the same-provider stratum was not independently significant (p = 0.151, one-sided exact test). JPEG-95 reduced the unchanged conjunction to 1/486 positives and zero controls. The native temporal hits were complementary to the signed period-8 hits, but the same-provider rate and codec collapse identify another export noiseprint rather than a runtime SynthID expert.

The separate OpenAI period-8 DTCWT component is persistent rather than tied to one short rollout: exact-generator asserted hits were 3/16, 46/365, and 26/200 from May through July, with 75/581 overall versus 1/52 same-generator rows without an assertion. Its native/JPEG minimum score reached 0.721 AUC between those indeterminate strata. Sorting all 64 cyclic correlation scores removed absolute phase but also removed locked-test discrimination at 0/158 positives and 0/135 controls. This remains research evidence for a weak signed carrier, not a runtime OpenAI detector.

A four-family open-proxy challenge also failed to justify a generic neural watermark expert. A fixed residual frontend and cross-family residual mixing were trained on three of TrustMark P, VideoSeal, DWT-DCT, and WAM while the fourth encoder and its test sources remained unseen. Held-out AUCs ranged from 0.437 to 0.562. Equal-power phase-scrambled hard negatives prevented simple spectral-energy shortcuts, but did not produce architecture transfer. A separate translation-invariant Gemini bicoherence search selected none of 20 development positives and finished at 0/50 positives, 0/199 controls, and AUC 0.374. Neither branch is part of runtime routing; full split and oracle details are in the detector research plan.

The separately measured registered geometry range remains 250,000 through 10,000,000 decoded pixels with both sides at least 256 pixels. The default path and identify use registered-v3, then the narrower opponent-registered-v1 fallback in its 1-10 megapixel domain, and large-v1 above 10 megapixels. A 20-image real-corpus drift check was byte-identical after the earlier v2 integration. The calibration history and caveats are in the linked detector research plan.

Official OpenAI SynthID verifier

openai_provenance.py provides the explicit remote production backend exposed as verify-openai-synthid. It is intentionally separate from identify, because one invocation uploads a sanitized raster to OpenAI. The CLI requires --acknowledge-upload, and the optional OpenAI SDK lives in the independent verify extra.

The backend accepts only PNG, JPEG, and WebP. It computes a decoded RGBA pixel fingerprint, removes AI provenance metadata into a temporary file through metadata.strip_and_verify, recomputes the fingerprint, and aborts before any request if metadata survived, the format changed, the pixels changed, or the sanitized file exceeds the endpoint's 50 MiB limit. It then sends exactly one multipart file to content_provenance_checks.create and parses exactly one type == "synthid" result. The independent C2PA entry is never returned or used as fallback evidence. Missing, duplicate, or unknown SynthID outcomes are errors rather than negative detections.

The default SDK client has a 120-second request timeout and zero automatic retries. One upload acknowledgement therefore authorizes at most one media transmission rather than inheriting the SDK's retry default. Request logs keep the endpoint, temporary basename, media type, byte count, timeout, retry policy, duration, HTTP status, error code, and request id when available, but omit the source path, image bytes, credentials, and decoded-pixel fingerprint.

OpenAIProvenanceError preserves the status, API error code, request id, Retry-After value, and a transient-only retryable flag. The library does not automatically act on that flag: an explicit caller invocation is required for every additional upload. Transport and schema failures remain errors rather than becoming not_detected or a local detector result.

The result remains provider-scoped and positive-evidence-only. not_detected does not mean human-created, and the official endpoint's published prohibition on repeated reverse-engineering or evasion queries prevents using this backend as an adaptive training or removal oracle.

Portable metadata record

metadata_record.py produces the record evidence_from_metadata_record consumes, so collection and verdict can run on different machines. Its contract is equality with the file path, and the three defects found while establishing that equality are the reason each rule exists:

• It walks the file's RAW head, never the scan_head buffer. That buffer is the head concatenated with late metadata payloads, so a structural walk runs off the end of the real head and parses appended bytes as chunks, inflating the record and creating false signals.
• Samsung Galaxy AI splits its evidence: the PhotoEditor_Re_Edit_Data marker sits in the post-EOI trailer while the genAIType value it is gated on can sit inside the entropy-coded scan. A marked file therefore keeps the whole tail window, not just the trailer.
• PIL's info keys are emitted in the file path's own candidate order (Software, Source, Title, Description, then EXIF). generator_from_metadata returns the FIRST candidate carrying a known token, so preserving candidate order is part of verdict equivalence.

The transport is independently versioned as provenance_metadata schema 1. Native records require the exact integer schema version and a complete status. Source read failures are explicit error records and cannot be judged. WebP walks the full declared RIFF container by seeking over VP8, VP8L, ALPH, and ANMF, so late XMP/C2PA remains visible without shipping coded frames or parsing appended trailer bytes as chunks.

Pixel forensics are deliberately absent: the provenance path does not read them. Verdict equivalence is checked over tracked fixtures and a separate local evaluation corpus.

Broad forensic metadata

forensic_metadata.py owns the wide metadata-only inspection record: hashes and timestamps, full EXIF/IPTC, C2PA, container inventories, bounded binary metadata, and embedded-thumbnail forensics. It is a separate forensic_metadata record type and is deliberately rejected by the provenance normalizer. Integration code publishes the strict ProvenanceReport.to_dict() alongside it rather than letting operational fields or derived results influence detection.

Pixel forensics

pixel_evidence.py measures six families of scale-robust pixel statistics (block-DCT histograms and Benford deviation, FFT band energies and CFA peaks, high-pass residual, error level, gradient, color) in a single decode, sharing the intermediate maps between them.

It remains independent of verdict and removal. PixelEvidence.to_dict() is the versioned service boundary: it omits the local path, exposes complete/partial/error status, keeps exception details in logs, and can include opt-in per-stage timings.

The provenance metadata collector, broad forensic collector, provenance report, and pixel report all accept an explicit output schema_version. Package releases may add an output schema while retaining older serializers, so a rolling consumer can keep requesting the version it already understands. Within one schema, changes are additive; existing fields, types, meanings, signal names, and watermark labels remain stable. Unsupported selections raise before a different shape is returned.

artifacts=True additionally returns the spatial layer: a perceptual hash, a 128px JPEG thumbnail, and coarse ELA, residual and phase maps. Those identify the source image rather than describe it, which is why they are opt-in and a separate field: a caller storing them is handling image content, not statistics about it.

The DWT-DCT detector and the visible-mark stage share a single decode of the source, held by a per-call _SharedDecode. It exposes two accessors because the two arms need opposite failure handling: the visible arm swallows a decode failure (no cv2, no visible marks, metadata verdict untouched), while the invisible arm re-raises it so has_invisible_target reaches its documented fail-safe True. Swallowing it there would skip a diffusion scrub on a file that used to get one. TrustMark deliberately keeps its own Pillow decode: cv2 and Pillow disagree on EXIF orientation and on 16-bit PNG, so substituting one for the other is not behavior-preserving.

The metadata probes (aigc_label, xai_signature, iptc_ai_system, huggingface_job, samsung_genai) and extract_c2pa_info are memoized on (path, mtime_ns, size). One identify reaches each of them twice, and each re-walks the container or re-runs the manifest reader. Size is in the key as well as mtime because this package rewrites files in place, and an in-place rewrite can land inside one mtime tick. The C2PA key additionally carries the reader-availability flag: with the official reader the manifest comes back as a store and without it from the PNG chunk parser, so the answer depends on process state and not on the file alone.

Native-container TC260 readers (isobmff, ebml, riff, flv) all run, in that order, on every file. Each self-gates on its own magic bytes after a 4-12 byte read, so gating the AVI and FLV ones on the file extension as well was redundant and made a correctly formatted container served under the wrong name invisible. WebP is the one input class the now-unconditional RIFF reader newly touches; its AVI form check is what rejects it.

api._SourceEvidence extracts that metadata once per remove_all call and serves both the visible pass (which vendor is confirmed) and the scrub gate (is there an invisible target). It is per-call, never module-level: batch may write its output over its input, and a holder that outlived one call would answer the scrub gate from pre-write evidence. In batch each stage builds its own holder after any write that precedes it, for the same reason. Every accessor fails safe the way the function it replaces does — no provenance means no relaxation, and an unknown invisible target means scrub rather than skip.

The detect extra composes the shared pixels runtime with PyWavelets. Its in-tree dwt_dct.py decoder reproduces the upstream algorithm's output bit for bit without installing Torch or non-headless OpenCV; the block scan is vectorized rather than transcribed, so the file no longer reads line by line against maxDct.py. The upstream MIT notice ships inside the wheel under licenses/.

is_ai_generated is True or None; absence of evidence is not reported as a human-made verdict. ai_source_kind distinguishes fully generated content from AI-enhanced composites when the source metadata provides that distinction.

TrustMark is reported as a watermark signal but does not by itself assert AI origin because it can also protect human-authored content. The decoder requests binary mode, matching Adobe's Durable Content Credentials example, then requires the same payload and schema after a quality-95 JPEG round-trip. Only Variant P schemas 0-2 count as positives. Schema 3 is below the precision threshold: all 38 measured historical false-positive candidates used it, and six retained the same false payload after re-encoding. The official Adobe Variant P schema-1 fixture in data/fixtures/provenance/ is the positive regression control.

Why the DWT-DCT decoder looks the way it does

Two things in dwt_dct.py are load-bearing and neither is obvious from the code.

_approximation calls pywt.dwt twice instead of pywt.dwt2, and transposes before each pass. A factorial ablation over both axes separates the two: skipping the three detail bands dwt2 computes and this code discards is worth 4%, while the transposes are worth 2.8x, because pywt walks the axis it transforms and on axis 0 of a C-contiguous plane that is a column walk. The arithmetic saving is the intuitive explanation and it is the small term; four independent profiles named it as the mechanism before the ablation contradicted them.

Bit-identity is a hard requirement, not a preference. For uint8 input the exact Haar LL value is a multiple of 0.5 and the bit test is peak % 36 > 18.0, a threshold sitting exactly on a representable value that ~1 block in 72 lands on, so a 1-ulp difference deterministically flips real bits. That is why the ~16x available from a hand-rolled numpy Haar is unreachable rather than merely untaken: pywt's C convolution contracts into an FMA that numpy has no ufunc for, and np.longdouble is 64-bit on arm64 macOS.

Each pass is one flat pywt.downcoef call over a raveled strip rather than pywt.dwt(..., axis=1)[0], and the plane is processed in strips of _STRIP block-rows so no full-plane float64 intermediate is ever materialized. The strip height is not a tuned value: 8 through 64 all scored inside each other's noise with unstable ordering, and only "strips at all" versus whole-plane matters.

_approximation's even-last-axis check is load-bearing, not defensive. Haar's filter is length 2, so an even row length keeps every pair inside its own row; on an odd width the pairs walk across row boundaries and the reshape still succeeds whenever the total is even, which would be wrong bits with no exception. Both call sites are even by construction today, and TestRaveledHaarPass pins both halves -- the downcoef/dwt equivalence, which a pywt upgrade could take away, and the raise on an odd width.

Measured on a 1536x2816 image, all arms timed in one process: the decoder went 0.112 s (the original per-block Python loop) to 0.011 s vectorized to 0.007 s with strips, and a warm identify() 1.757 s to 1.365 s on the first step and a further 0.4% on the second. That last figure is the point at which this target is finished: the decoder is now under 2% of identify(), so speed here has stopped buying anything. What the strips buy is peak RSS in the stage, 111 MB to 21 MB on a 4.3 MP image, which is what matters on the memory-limited Space.

Both steps were verified by recording decoder output and detector verdict over 200 sampled data/ images plus two synthesized carriers before and after: the record is byte-identical, as are seven degenerate shapes (1x65536 through 8x8192, plus an odd width) that clear the caller's area check.

Regression coverage:

• test_identify.py
• test_trustmark_detector.py
• test_invisible_watermark.py -- note test_in_tree_decoder_matches_upstream is the parity guard against upstream's own decoder, and the whole module is skipif(not is_available()). A green run without the detect extra installed has not checked parity at all, so a decoder change still owes the before/after verdict record.

Visible mark removal

Registry and decision flow

watermark_registry.py is the only visible-mark registry. mark_keys() supplies the CLI choices, so the CLI must not maintain a separate mark list.

Automatic removal has three distinct stages:

1. Perception: each registered detector produces strict and relaxed candidates.
2. Decision: the pure decide arbiter applies sensitivity and corroborating provenance.
3. Action: each selected mark is localized to a mask and passed to the shared fill function.

sensitivity="strict" never relaxes a detector. sensitivity="auto" can relax one only when metadata or a sufficiently strong same-product sibling confirms that product. The removed blanket assume_ai mode is rejected explicitly.

The Jimeng pill has an additional decision gate because its visual detector is weaker than the other registered marks. Keep that policy in the registry, not inside unrelated detector engines.

Everything about a mark is one registry row: its product family, its label regime, the platform sentence identify reports for it, and the metadata signals that confirm its vendor. identify._VISIBLE_MARK_PLATFORM and the signal mapping in api.visible_provenance are derived from those rows rather than hand-maintained beside them, so registering a mark is one edit. Two marks carry no platform of their own: the Gemini sparkle has its own higher-confidence path, and the capture-less pill is too weak to attribute.

The set of marks that veto the pill is DERIVED from the registry rows: every mark under the same label regime (tc260) belonging to a different product. It used to be a hand-written list of keys, and that list drifted -- LiblibAI was registered alongside RunningHub and Baidu, both of which were added to it, and LiblibAI was not, so a confident LiblibAI detection did not suppress the pill the way its two siblings did. Marks outside the TC260 regime (Gemini, Samsung) are deliberately not vetoers: neither can put jimeng into provenance, so neither can enable the arm it would be vetoing.

A TC260 label relaxes the vendor its ContentProducer names, resolved through KnownMark.tc260_producer_codes. The label itself is vendor-agnostic, so this used to relax ByteDance's two products on every China-AIGC image -- which both risked a false fill on an image carrying some other vendor's mark and denied that vendor's own mark the relaxed gate its provenance_ncc_factor was calibrated for. An absent or unmapped producer still falls back to the ByteDance pair.

remove_auto_marks removes every selected mark, not only the strongest one. This matters for images that carry marks in more than one corner.

Regression coverage:

• test_watermark_registry.py
• test_api.py

Gemini sparkle

gemini_engine.py uses a multi-scale shape search and a false-positive gate. Its captured sparkle assets serve detection and mask geometry only. Pixel recovery is performed by the shared fill backend.

detect_sparkle_confidence uses a process-wide shared engine because its loaded assets and template ladder are immutable.

Regression coverage:

• test_gemini_engine.py

Text mark engines

_text_mark_engine.py provides common localization, detection front ends, template caching, rival comparison, and footprint construction.

Each vendor module supplies a TextMarkConfig and only the behavior that cannot be represented by the shared base:

• doubao_engine.py
• jimeng_engine.py
• qwen_engine.py
• kling_engine.py
• yuanbao_engine.py
• samsung_engine.py
• runninghub_engine.py
• baidu_engine.py
• liblib_engine.py
• microsoft_engine.py

The measured Microsoft badge variant (2026-08-27 registration) is the first tr-corner mark and the first long-side scale basis: the pill tracks the render dimension, so a 1024x1536 portrait carries the same pill as 1536x1024, and a width basis undersized the template by the aspect ratio (portrait carriers fell to 0.15-0.32 NCC until the basis was measured). The silhouette is a white pill with its synthetic internal shapes knocked out - the holes are what separate it from any other bright rounded corner element (a plain white pill scores below the gate in the tests). It does not claim coverage of Microsoft's other documented icon, wording, or position variants.

The 2026-08-27 rerun used the registered engine through scripts/registered_mark_calibrate.py, rather than a copied detector configuration. The manifest kept three evidence classes separate: 17 visually confirmed carriers, 343 Microsoft-provenance files without a visual adjudication, and 1200 non-overlapping no-signal controls. At the strict 0.38 gate, 15/17 confirmed carriers fired (min 0.249, p50 0.519, p90 0.578, max 0.579), while 0/1200 controls fired (p99 0.200, max 0.293). The provenance cohort produced 78/343 fires, but that is not a recall measurement because provenance identifies the provider, not the presence of this visible layout. That cohort was later labeled by an OCR badge census (2026-08-28: 86 badge carriers, 257 badge-less, badge-less max 0.251 / p99 0.213), which is what enabled the shipped provenance relaxation 0.7: the relaxed band [0.251, 0.38) holds three faint badges and zero false fills, re-verified as 3 band detections with 0/257 badge-less fires on the provenance path.

The detector and removal mask must use compatible geometry. A detector that fires while producing an empty or misplaced mask is a removal failure even if the detection test passes. That parity is now structural rather than a convention: the three continuous front ends share one ladder sweep (_ladder_best), and the winning box travels to the mask on TextMarkDetection.match_box instead of being swept a second time.

Detection is split into a trust-level-blind _scan and a _verdict that applies the threshold. detect_both returns the strict and relaxed verdicts from one scan, which is what the arbiter's perception stage calls. A per-mark demotion belongs in the _post_gate hook, never in a detect override: an override is invisible to the single-pass path, and the RunningHub and Yuanbao anchor gates were briefly skipped there for exactly that reason.

A mark whose removable footprint differs from what the detector localizes overrides _footprint_rect (which policy) and _extend_match_box (how far the box grows), not the whole footprint_mask. Baidu extends right to the corner tag and LiblibAI extends left to the triangle logo; both inherit every guard around that arithmetic.

Yuanbao uses the polarity-independent contrast front end because its standard two-line mark can be light on dark scenes or dark on light scenes. Its detector and footprint both use the same best-match box. The separate one-line overlay variant is not covered.

The capture-less Jimeng pill lives in pill_engine.py. It uses a synthetic silhouette for detection and a fixed top-left footprint.

Each engine has a corresponding test module under tests/. Shared behavior is covered by:

• test_text_mark_engine.py
• test_text_mark_faint_mask.py
• test_text_mark_memory.py

Fill backends and region erasing

region_eraser.py implements the same backends used by visible removal and the user-directed erase command:

• cv2
• migan
• lama

watermark_registry.resolve_backend selects LaMa first, then MI-GAN, then OpenCV for auto. A memory-constrained caller should explicitly select MI-GAN or OpenCV instead of relying on auto.

MI-GAN and LaMa crop around the mask before model inference and paste back only masked pixels. Their model sessions are loaded lazily. MI-GAN uses the inverse mask polarity expected by its ONNX model.

Regression coverage:

• test_region_eraser.py
• test_inpaint_fallback.py

Invisible watermark regeneration

Profiles and strength

_internal/watermark_profiles.py is the source of truth for:

• profile names and their underscore spellings;
• the fixed seed;
• the SDXL global-stage checkpoint id (SDXL_MODEL_ID) and the Canny ControlNet id;
• strength resolution for both profiles.

The current profiles are qwen-zimage (the default) and sdxl-zimage, and both are CUDA-only. controlnet, sdxl, qwen and default were removed rather than kept as a CPU path, and are rejected rather than aliased onward. There is no content-dependent automatic router.

qwen-zimage normally resolves global denoise from image area for unknown content. Measured provider cohorts bypass that curve with flat operating points. The values, measurement derivations, and corpus limits are canonical in known-limitations.md.

For serverless cold starts, InvisibleEngine.preload(global_only=True) loads the mandatory global stage and YuNet while leaving the optional Z-Image and SAM face stack lazy until a face is detected. The default preload() still loads every stage.

What is deliberately not a parameter. Model id, step count and CFG are fixed by the profile, so none of them appears in WatermarkRemover.__init__, remove_watermark, InvisibleEngine, or the CLI. They used to be accepted and then rejected several frames down; a signature that refuses the argument outright fails where the caller can act on it, and stops a wrapper from threading a value that would silently do nothing. The step count and CFG live with the stage that runs them (GLOBAL_STEPS, FACE_STEPS, GLOBAL_CFG, FACE_CFG in qwen_zimage_pipeline.py). The dtype is likewise profile-owned: see "Face-stage dtype" for what an override cost the last time one existed.

device is the exception and remains a library parameter: None or "auto" detect, "cuda" pins without detecting (which is what a container that knows its hardware wants), and any other value raises at construction. It is not a CLI option, because the only useful value a user could type is the one detection already returns.

invisible_engine.py handles image sizing, postprocessing, and the public engine interface. It delegates model execution to _internal/watermark_remover.py.

get_device in that module answers only cuda or cpu. An mps or xpu answer would travel one frame to the same CUDA-only refusal while costing a device probe, and reporting it implied an Apple-silicon or Intel-GPU path that does not exist. The refusal names the resolved device, so device=None on a CUDA-less host says 'cpu' rather than 'None'.

The Python engine and the CLI now resolve the same defaults: the CLI forwards an unset --adaptive-polish and --seed as None and the engine applies the profile's answer, so a library caller and a CLI caller on one profile produce the same pixels. They diverged before, in opposite directions, for exactly this knob.

The global and face prompts are calibrated model inputs, and the Canny edge map uses fixed thresholds of _CANNY_LOW = 13 / _CANNY_HIGH = 64 (qwen_zimage_pipeline.py). Treat those values as behavioral compatibility contracts: a refactor must preserve them, and any deliberate change requires image-quality evaluation rather than only a unit-test pass. The prompt and edge-map regression guards are test_qwen_zimage_pipeline.py::test_global_kwargs_use_lightning_and_diffsynth_controlnet_shape, ::test_face_kwargs_use_project_zimage_settings and ::test_canny_control_image_is_three_channel_and_detects_an_edge.

Regression coverage:

• test_invisible_engine.py
• test_qwen_zimage_pipeline.py
• test_platform.py

CPU offload

CPU offload is enabled only when requested. Nothing calls Diffusers' enable_model_cpu_offload any more -- that belonged to the deleted single-stage profiles. --cpu-offload now forces both stacks of the two-stage profiles out of automatic device residency.

Residency is otherwise chosen from the card's total VRAM, once per stack: resolve_global_model_residency gates the mandatory Qwen stack at RESIDENT_GLOBAL_MODEL_MIN_VRAM_GIB and resolve_face_model_residency gates the optional Z-Image stack at RESIDENT_FACE_MODEL_MIN_VRAM_GIB.

Below the global floor, _qwen_vram_config streams the stack from disk, which is what makes a 20B model runnable on a consumer card. At or above it, streaming is pure waste and the weights stay on the GPU. The difference is not marginal: DiffSynth offloads by dropping the weights to the meta device and re-reading every parameter through its DiskMap on the next onload, and the pipeline moves between text encoder, transformer and VAE on each pass. Measured on an H100 (80 GiB) in August 2026, a warm global pass took 37.3 s at 0.8 GiB resident with the streaming config, against 2.2 s at 28.7 GiB with the stack resident; both stacks resident peaked at 48.0 GiB. Faster storage cannot close that gap, because the cost is the reload itself rather than the read.

The resident config deliberately passes no "disk" value anywhere. DiffSynth latches disk_offload once, from offload_dtype, so leaving the sentinel in place while pointing every device at CUDA would keep the meta-drop and re-read.

Regression coverage:

• test_cpu_offload.py
• test_qwen_zimage_pipeline.py

Qwen plus Z-Image

_internal/qwen_zimage_pipeline.py implements the fixed CUDA-only two-stage profile:

1. Qwen Image with Canny conditioning regenerates the frame.
2. YuNet locates faces, SAM builds masks, and Z-Image regenerates the selected face regions.

The profile rejects a custom model identifier. Its global and face model stack is fixed by the implementation. When tiling is enabled, only the global stage is tiled; the face stage runs once after the tiles are blended.

How the face stage actually composites

The mechanism is easy to misread from the parameter names, so state it plainly. _run_faces crops the expanded box from the original image, resizes it toward the 768 px face guide, runs Z-Image over the entire crop, resizes back, and only then merges through composite_face, which cross-fades on a Gaussian-blurred SAM mask with feather=10. The base it merges into is the global Qwen result.

Two consequences follow, and both matter when tuning:

• Everything inside the crop is regenerated, including the pixels the mask later discards. The generation is therefore conditioned on a fully noised neighbourhood, not on an intact one. An alternative design passes the mask into the sampler as a latent noise mask, so only masked pixels are ever denoised and the edge transition happens inside the generation rather than as a post-hoc blend. That approach has never been tried in this runtime and is an open lever, particularly since the face stage is the largest measured quality contributor: removing it costs 3.5 dB inside the face boxes on one fixture and 6.1 dB on another.
• FACE_DENOISE_SCALE = 0.5 is best understood as compensation for the above. Regenerating a whole crop and blending is a stronger operation than denoising only inside a mask, so the halved strength brings the visible result back into range. Read it as coupled to the compositing design rather than as an independently calibrated constant: changing the compositing without revisiting the scale would change output strength by roughly a factor of two.

The maintained implementation preserves the previously oracle-tested strength, conditioning, crop, and sampler parameters as compatibility contracts. Its Python orchestration, YuNet integration, SAM selection, masks, sizing helpers, and pixel compositing are implemented for this runtime. Changing a calibrated model input requires the same provider-oracle and identity evaluation as a model change.

Verified text restoration

_internal/text_restoration.py implements the opt-in vae-glyphs stage. A versioned manifest carries manually reviewed strings and source-space line boxes in schema 1, or verified source-space geometry alone in schema 2, plus a SHA-256 over decoded RGB width, height, and pixels. Validation happens before model loading. The library never treats OCR confidence as verification, and geometry-only operators do not need to invent text or script fields.

When enabled, QwenZImagePipeline reconstructs the source once through its already loaded Qwen VAE, runs the ordinary global and face stages, and calls the shared restoration compositor. The optional fidelity anchor first blends 15% of the VAE reconstruction into the clean result; it is off by default because the blend returned detector-visible OpenAI SynthID in the measured poster fixtures. The compositor derives binary source and candidate silhouettes, groups nearby lines, uses LaMa for the initial and residual-glyph erase passes, paints fresh silhouette edges, then copies the Qwen-VAE core with a 0.5-pixel feather. The evaluation script imports these same mask and compositing helpers so the two implementations cannot silently drift. Silhouette crops start 12% of line height beyond each horizontal side, then expand each side independently while a foreground component anchored inside the detector box still reaches that boundary, up to one line height. They extend 8% above and 25% below. The anchored-component gate covers clipped leading flourishes, trailing punctuation, icons, and descenders without walking into disconnected decoration or background texture.

The stage is deliberately narrower than the engine: it rejects sdxl-zimage, tiles, resolution caps, humanize, unsharp, and adaptive polish. Those combinations change geometry or final pixels after the verified layer and have no measured oracle result. It remains opt-in because annotations are manual and provider verdicts apply only to the exact tested output hashes, not to the mechanism in general.

A matched stage-isolation check on the 18-face Gemini portrait grid confirms the division of responsibility. The visible-cleaned, metadata-stripped control and the Z-Image face-only output were both SynthID-positive; Qwen global-only and the full Qwen-then-Z-Image output were both clean. The face stage raised identity cosine from 0.589 to 0.852 and reduced face LPIPS from 0.217 to 0.050 without reintroducing a detectable whole-image signal. Thus Z-Image is a masked fidelity repair stage here, not the watermark-removal stage. Exact hashes, metrics, strengths, and the one-fixture, one-seed caveat are recorded in data/evaluations/fidelity/face-stage-isolation-2026-08-13.csv.

The public Synthid-Bypass v2 graph was subsequently audited at upstream commit 3007d035. Its saved-output path confirms the same division: Qwen-Image-2512 Lightning plus Canny is global, and Z-Image Turbo exists only inside the masked face detailer. The connected face path is YOLOv8-face plus SAM; the MediaPipe nodes described by the upstream README and the 1.2-megapixel normalization node do not reach SaveImage. Upstream also applies its adaptive face strength directly, whereas this implementation multiplies it by FACE_DENOISE_SCALE = 0.5.

A close reproduction on the same portrait fixture kept the control positive and made both Qwen global-only and full Qwen-then-Z-Image outputs clean. Applying the upstream-strength face pass raised identity from 0.589 to 0.783 and reduced face LPIPS from 0.217 to 0.083, but remained worse than this profile's 0.852 and 0.050. The published upstream pair 12 was also independently checked positive before and clean after, with 0.975 identity. Exact workflow provenance, hashes, metrics, oracle outcomes, and the DiffSynth/GGUF, scheduler, detector, and seed caveats are recorded in data/evaluations/fidelity/upstream-v2-reproduction-2026-08-13.csv.

SDXL plus Z-Image

_internal/sdxl_zimage_pipeline.py runs the same two-stage recipe on an SDXL global pass. SdxlZImagePipeline subclasses QwenZImagePipeline and overrides only _run_global and preload, so the face stage is inherited rather than copied and cannot drift between the profiles; a test asserts the shared methods are the same objects.

Four things are architecture-bound and swap with the model: the ControlNet (xinsir/controlnet-canny-sdxl-1.0), the four-step distillation LoRA (ByteDance/SDXL-Lightning at its documented strength 1.0, not the reference graph's 0.8, which belongs to a different LoRA), the sampler (Euler with trailing spacing, no AuraFlow shift), and the latent grid (8 px against Qwen's 16).

Strength is architecture-bound too, and that is the easy mistake. An SDXL global pass leaves SynthID at the strength Qwen needs: verified through the Gemini app on a native 2816x1536 original, 0.154 is FOUND while 0.20, 0.25 and 0.30 are clean. So this profile takes a vendor policy (SDXL_ZIMAGE_OPENAI_STRENGTH 0.15, SDXL_ZIMAGE_GEMINI_STRENGTH 0.25, unknown following Gemini) rather than resolution_adaptive_denoise. Flat values are what was measured; no size dependence has been established for this stage, so none is asserted.

requested_steps exists because the two runtimes truncate differently. DiffSynth sets sigma_start = denoising_strength and runs every requested step across the shortened sigma range; Diffusers img2img truncates the step count (init_timestep = int(steps * strength)), so asking it for four steps at 0.15 executes zero and returns a bare VAE round-trip.

The face stage keeps its own dtype, and 0.23.0 shipped without that. The remover gives this profile torch.float16, because SDXL ships fp16 weights and an fp16-safe VAE. That dtype reached the inherited _load_zimage, while _zimage_vram_config() hardcodes bfloat16 for its offload, onload and computation dtypes -- so the Z-Image modules were built bf16 and handed fp16 latents, and every image containing a face died in the VAE with Input type (c10::Half) and bias type (c10::BFloat16) should be the same. Every face-stage loader now reads _face_stage_dtype(), which returns the computation dtype of the VRAM config it is paired with, so the two cannot drift again.

Two things hid this. Zero-face inputs never enter _run_faces, so the profile looked healthy on exactly the images used to time it; and the profile's tests deliberately avoid model downloads, so nothing exercised the loader. The lesson is narrower than "add a GPU test": inheriting a stage means inheriting its invariants, and this one was a dtype the subclass silently changed out from under it.

Note what the seam is, because it decides where the fix belongs. SdxlZImagePipeline._load_sdxl hardcodes fp16 for its own ControlNet, VAE and pipeline, so self.torch_dtype was never actually the global stage's dtype on this profile -- its only remaining readers were face-stage code. SAM was the second one: it never crashed, because it casts its own inputs and leaves through .float(), but it was reading the same wrong field and would have re-landed the bug for the next profile with a different global dtype. It is routed through the same accessor, which for qwen-zimage is the bfloat16 it already used.

The guard is test_face_stage_loads_in_its_own_dtype_when_the_global_stage_differs. It asserts the dtype the Z-Image and SAM loaders actually receive, not the accessor against the config it is derived from -- that comparison would restate the implementation and pass for any consistently wrong value. Both assertions were mutation-tested against the pre-fix line. For qwen-zimage the whole change is a strict no-op: the remover already handed it bfloat16, the same value _face_stage_dtype() returns.

This profile is not deployed. Before it could be, it needs the other three Gemini originals, OpenAI re-verified at 0.15, a flat-graphic content class, and a low resolution case -- every verdict so far comes from one fixture and one seed.

Measured provider boundaries for qwen-zimage

Both ends of the shipped curve now have oracle verdicts, and the shipped curve clears everything it has been tested at:

oracle	fixture size	detected at	clean from
openai.com/verify	1.57 MP	0.06	0.08
Gemini app	4.33 MP	0.08	0.10
Gemini app	0.57 MP	--	0.0896 (the curve's own value)
Gemini app	1.40 MP	--	0.1066 (the curve's own value)

Read the last two rows before concluding the curve's low end is under-driven. Against the 4.33 MP Gemini boundary the sub-1 MP rungs of 0.084-0.098 look short, but at those sizes the curve's own values verify clean, which is what a resolution-scaled requirement would predict. There is no measured size at which the shipped curve fails, so it is left alone.

Meta Content Seal boundaries for qwen-zimage

Measured 2026-08-26 against the anonymous oracle meta.ai/identification (verdicts read from the settled page text; corpus and full row-level provenance in data/contentseal/manifest.csv). Muse Image carries no C2PA, so vendor_for_strength returns None for it and these images ride the default resolution-adaptive curve; there is deliberately no meta entry in the flat vendor map, because no provenance signal can establish that cohort automatically and an unreachable constant would be dead code.

source (2.56 MP generation)	detected at	clean from
gen_lighthouse_watercolor	0.0525	0.06
gen_fox_forest	0.03	0.0375
gen_night_city	0.03	0.0375
gen_studio_mug	--	0.03
gen_text_poster	--	0.015

Full spread: worst first-clean boundary (0.0525, 0.06] on lighthouse, easiest source already clean at 0.015. Following the same derivation as the OpenAI and Microsoft floors (worst clean boundary plus one full observed cross-source spread): 0.06 + (0.0525 - 0.015) = 0.0975, rounded up to 0.1. Shipped as QWEN_ZIMAGE_META_STRENGTH with two routing paths: auto mode routes a file whose only provenance is the standalone AI IPTC tag onto the cohort (vendor_for_strength checks C2PA issuers first, so Google/OpenAI/Microsoft evidence always wins, and the tag's other users ship no invisible watermark this profile targets), and --vendor meta / InvisibleOptions.vendor names the cohort explicitly on stripped files, implying the scrub runs (naming the cohort asserts the watermark is present). sdxl-zimage has no measured Meta rung and an explicit meta vendor there falls to the conservative unknown 0.25. The default resolution-adaptive curve (~0.1305 at 2.56 MP) also clears every measured source, so default behavior needed no change. Oracle verdicts carry a generation ID and creation timestamp embedded in the watermark payload; both survived the 512 px resize and JPEG q85 rows, so payload recovery outlives the detection threshold. Oracle session limits are per-IP, server-side, and sliding-window: clearing cookies and storage does not reset them, and a burst exhausts the window minutes after it reopens.

Static prompt embeddings

Both stages prompt with module constants, and at CFG 1.0 DiffSynth's PipelineUnitRunner reuses the positive embedding for the negative side instead of encoding it. So exactly one embedding per stage is ever computed, from text that cannot vary at runtime, which makes it cacheable across containers rather than only within one pipeline.

_cache_static_prompt_embeddings therefore persists what the text encoder produced under _model_cache_dir()/prompt-embeddings, keyed by cache version, model id, pipeline output params, and the exact prompt string. Once that file exists, _load_qwen and _load_zimage drop the text-encoder ModelConfig from the model stack entirely and serve the stored tensors instead. Measured on an H100 volume in August 2026, that removes 15.45 GiB (Qwen2.5-VL) and 7.49 GiB (Z-Image) of a 87.6 GiB per-request read, worth a median 11.76 s and 4.10 s of load time (paired within five containers). The output is byte-identical -- the stored tensors are the encoder's own -- so this needs no provider-oracle re-verification.

Three properties are load-bearing:

• The key self-heals. A model bump or a prompt edit changes the key, so the next container recomputes rather than reading a stale embedding. _PROMPT_CACHE_VERSION covers a change to the stored shape itself.
• The write is atomic. A torn write must never be readable as a cache hit, so the payload lands in a temp file and is renamed into place.
• A miss after the encoder was dropped raises. require_cache records that the stack was built without a text encoder on the strength of the file; falling back would call a model that is not loaded, which surfaces as an opaque crash.

_model_cache_dir() prefers HF_HOME for the same reason: on a scale-to-zero runner that is the only persistently mounted path, and anything below it is re-derived per request. The YuNet download follows the same root.

Regression coverage:

• test_qwen_zimage_pipeline.py
• test_cpu_offload.py

Tiling

_internal/tiling.py contains pure tile planning, feather weights, and tile orchestration.

Tiling engages only when requested and the long side exceeds the tile size. It avoids an explicit full-image downscale but does not make diffusion pixel-preserving. Each tile is still regenerated.

It also held a feather_region_composite for AI-enhanced composites, where only the edited region should change. Nothing ever reached it: the erase command inpaints through region_eraser, and the remover's region argument was only reachable from a module-level convenience wrapper with no callers. Both went.

Regression coverage:

• test_tiling.py

Postprocessing

humanizer.py contains explicit grain, unsharp masking, and adaptive polish helpers.

upscaler.py held an optional Real-ESRGAN path, reachable only when enlarging a small image to the minimum-resolution floor. That floor existed to lift small inputs toward SDXL's ~1024 training size; when the SDXL profiles were removed it was forced to 0 on every path, so the module, the --min-resolution and --upscaler options and the esrgan extra were all unreachable and went with it. Only the max_resolution cap can move geometry now, and it only scales down.

Regression coverage:

• test_humanizer.py

Image input and output

image_io.py is the shared image codec boundary.

Contracts:

• All package OpenCV file reads and writes use image_io.imread and image_io.imwrite.
• to_bgr normalizes grayscale and alpha-bearing arrays.
• read_bgr_and_alpha and write_bgr_with_alpha preserve the alpha plane.
• imwrite returns a success flag; every caller must check it.
• HEIC, HEIF, and AVIF pixel reads fall back to Pillow plus pillow-heif from the independent heif extra. Metadata scanning does not require that plugin.
• A visible no-op can preserve the original file bytes.

Regression coverage:

• test_image_io.py
• test_cli_robustness.py

Adding or changing behavior

For a new visible mark:

1. create a synthetic detection silhouette;
2. add or extend a vendor engine;
3. add one registry entry;
4. test detection, false positives, localization, and actual pixel change;
5. update supported signals.

For a new metadata signal:

1. add the scanner;
2. add every supported removal placement;
3. verify the output through strip_and_verify;
4. add identification and removal tests;
5. update supported signals and, when relevant, the watermarking landscape.

For a diffusion change:

1. keep model-free logic in pure helpers where possible;
2. test option propagation and dispatch without downloading models;
3. run a real model smoke for the changed model path;
4. treat provider-verifier results as specific to the exact checked output;
5. update known limitations.