Grow the SynthID corpus to 109 originals (91 iPhone-photo negatives,
2 positives) and document what was learned studying 8 platforms:
- README: per-platform watermark map (C2PA issuer / SynthID pixel / IPTC
/ visible sparkle per platform) and an "originals, not previews" note
(re-encoded previews strip metadata, so a clean preview is not proof).
- CLAUDE.md: surface-dependent blind spot -- the same Google model wraps
C2PA in the Gemini app but emits the SynthID pixel watermark + sparkle
with no C2PA/IPTC via the API/playground (AI Studio, Nano Banana), so
synthid_source returns None despite SynthID being present; only the
pixel oracle or the visible-sparkle detector catches those.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Adds content positives (OpenAI gpt-image: forest, fisherman, tokyo; Google
gemini: fisherman, mug) and SDXL/non-SynthID negatives to the local corpus
manifest. Now spans 4 resolutions across 2 vendors (was solid-black only).
README: documents driving generation via Chrome MCP -- Gemini single-click
download; ChatGPT via in-page fetch+blob (preserves original C2PA bytes,
unlike the flaky UI download / a canvas re-encode).
Images stay gitignored; only the manifest (sha256 + labels + extracted
metadata) and protocol are tracked.
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