Lab: C2PA / Content Credentials#

Current status: Partial · Detect: Partial · Remove: Partial · Last tested: 2026-08-13

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What this signal is#

C2PA (Coalition for Content Provenance and Authenticity) defines a standard for embedding a cryptographically signed manifest in a file -- a record of how content was created or edited, optionally including "generated by AI" assertions. The manifest is packaged in a JUMBF container (ISO/IEC 19566-5): a JPEG APP11 marker segment, or a PNG caBX chunk.

MarkMyAss's C2PA support is explicitly labeled Partial, and stays that way regardless of individual test outcomes. This is a capability-level statement, not something a single clean/verify run can upgrade.

What MarkMyAss can test#

MarkMyAss's own detector scans for the JUMBF container structure itself (the APP11 segment / caBX chunk), NOT the manifest's contents. Presence of the container is a strong signal that a C2PA manifest exists; absence is a strong signal that it doesn't -- but this is a structural, byte-level scan, not a spec-conformant C2PA parse. Implementation: src/ghostmark/detectors/c2pa.py.

What MarkMyAss can remove#

The JUMBF container segment/chunk is deleted from the file (JPEG, PNG). This reliably removes a C2PA manifest embedded via the standard container MarkMyAss scans for -- it is not an audited guarantee against every possible embedding technique a future or unusual C2PA implementation might use. Implementation: src/ghostmark/cleaners/c2pa.py.

PDF: detection uses a raw byte-signature scan (looking for c2pa/jumb markers); cleaning is not implemented for PDF.

What MarkMyAss cannot test#

Cryptographic signature or trust-chain validation. Neither MarkMyAss's own detector nor its use of c2patool performs signature verification against a trust list. "No manifest found" is not the same claim as "this content's provenance chain, if any, is valid" -- those are different questions entirely.
Manifests embedded via non-standard containers MarkMyAss doesn't scan for.
Whether removing the container also removed every trace referenced elsewhere in the file (e.g. a cross-reference in a custom XMP field) -- MarkMyAss's cleaner targets the JUMBF container specifically.

Verification methodology#

Independent verification uses c2patool, the official Content Authenticity Initiative CLI, in its default read-only mode (c2patool FILE, no -m flag -- it never signs or modifies anything). MarkMyAss uses c2patool only to confirm presence/absence of a manifest, matching the scope of its own heuristic detector -- this is explicitly not a claim that c2patool cryptographically validated anything. Implementation: src/ghostmark/independent_verify.py (C2paToolVerifier).

c2patool is optional and licensed Apache-2.0/MIT; MarkMyAss never vendors it, only shells out to a separately-installed binary (see THIRD_PARTY_LICENSES.md). If it isn't installed, MarkMyAss says so rather than guessing.

Reproducible test commands#

ghostmark inspect photo.jpg --json    # look for the "c2pa" detector entry
ghostmark clean photo.jpg
ghostmark verify photo.ghostmark.jpg --receipt receipt.json

# Independently, with c2patool directly (read-only):
c2patool photo.jpg
c2patool photo.ghostmark.jpg

Covered by tests/test_images.py (synthetic JUMBF-marker fixtures) and tests/test_independent_verify.py (mocked c2patool behavior, including the "no manifest" and genuine-error paths).

C2PA Remover -- the practical, action-oriented version of this page.
Content Credentials Remover -- same mechanism, written for people who know the "cr" icon rather than the C2PA spec name.

Sources#

Something outdated or inaccurate?#

Open an issue or submit a pull request against src/ghostmark/web/content/lab/c2pa.md.

Last reviewed: 2026-08-13