scripts/synthid_pixel_probe.py is an experimental/diagnostic tool for the
one pixel-domain question that isn't a dead-end: on solid-color fills the
zero-mean residual IS essentially the watermark carrier. Two modes:
'consistency' (mean pairwise NCC of carriers across fills vs random
baseline) and 'removal' (does the pipeline drop the carrier toward
baseline?). Logic validated synthetically (injected carrier correlates,
random noise doesn't, simulated removal collapses it) -- no real fills or
GPU needed.
Running its metric on the corpus independently re-confirms the documented
dead-end for real content: at matched resolution SynthID positives do not
cluster apart from negatives (within-Gemini 0.07; at 1024 px pos-vs-neg
>= pos-vs-pos). An apparent 0.62 among 1254px ChatGPT positives turned out
to be near-duplicate content (5 renders of one prompt at ~0.92; a distinct
ChatGPT image scored ~0 against them), not a shared carrier. The probe is
solid-fills-only; do not use on real content.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
PIL cannot open iPhone HEIC without pillow-heif, so width/height stayed
0 for those negatives. Fall back to sips -g pixelWidth/pixelHeight on
macOS when PIL fails; returns (0,0) elsewhere.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Detect SynthID-bearing images via their C2PA companion: a manifest signed by a
SynthID-using vendor (Google/OpenAI) on AI-generated content implies an
invisible SynthID pixel watermark. Verified end-to-end against the vendor
oracles (openai.com/verify, Gemini "Verify with SynthID").
- metadata: synthid_source() + synthid_watermark verdict in get_ai_metadata,
surfaced as a `metadata --check` callout. Format-agnostic (PNG caBX parser +
JPEG/WebP/AVIF/HEIF/JXL binary scan).
- constants: SYNTHID_C2PA_ISSUERS {Google, OpenAI}; +opened/placed actions.
- c2pa: single CBOR-aware parser (_cbor_text_after) replaces glitchy regex
(fixes fGPT-4o claim_generator); removed duplicate _scan_png_c2pa_chunk from
metadata; shared synthid_verdict / synthid_vendors_in helpers.
- corpus: scripts/synthid_corpus.py ingest tool + data/synthid_corpus/
(manifest tracked, images gitignored) for a labeled reference set.
- tests: +38 across C2PA parser internals, extract/inject round-trip, ISOBMFF
container stripping, all IPTC AI markers, and invisible watermark strength
tiers (SynthID/StableSignature/TreeRing/StegaStamp/RingID/RivaGAN/...).
Pixel-level SynthID detection remains out of reach locally (Google's decoder is
proprietary); a from-scratch spectral pilot confirmed it does not separate real
content. See CLAUDE.md for the full evaluation.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
test-user