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Glossary

Hard binding: the hash that ties a signature to the pixels

A hard binding is the cryptographic hash of the asset’s content, excluding the manifest itself, recorded inside a signed C2PA claim, so that a validator can recompute the hash and prove the content has not changed since the manifest was signed.

Definitions and isGenAI behaviour as of October 2026. Updated .

See the term in a real reportFrequently asked questions
Code-drawn illustration for Hard binding

Illustration · PNG file

  1. Signature + IHDR
  2. iTXt XML:com.adobe.xmprecord
  3. tEXt parameters
  4. tEXt prompt / workflow
  5. tEXt invokeai_metadata
  6. eXIf
  7. caBX C2PA manifest
  8. IDAT pixels
  9. IEND

AI source type declared

The file labels itself as AI-made.

IPTC DigitalSourceType such as trainedAlgorithmicMedia is read from XMP and shown with its exact value.

Check an image →
AI source type declared: where this record sits inside a PNG file and what the isGenAI report says about it. The picture is a code-drawn illustration.

How it works

A data-hash assertion lists the byte ranges hashed and their digest; for ISO base media files a BMFF hash assertion covers the boxes; for some formats a general box hash is used. The claim references these assertions and is signed. If any covered byte changes, recomputation fails and the validator reports a hash mismatch, which is how editing, cropping, compressing or re-encoding after signing is detected. The manifest bytes are excluded so the manifest can be inserted after hashing.

What isGenAI reports

The C2PA checker reports cryptographic validation separately from trust: a valid signature with matching hashes is intact; a valid signature with mismatched hashes is reported as content changed after signing. Black Forest Labs and other vendors warn that editing or compression after signing produces exactly this result, so a mismatch usually means a copy, not a forgery, but either way the record no longer vouches for these pixels.

Hard versus soft

Hard binding is exact and fragile; soft binding is approximate and durable. A complete verification system uses both, and isGenAI’s report shows which one produced each finding.

For video, the BMFF hash can cover the file in chunks, which lets a validator check large media without hashing everything at once and report which part changed. The C2PA checker reports the validation codes for the parts that failed.

How to use this term when checking a file

  1. Upload the original file to the AI image detector or the tool named on the page.
  2. Find the finding that uses this term under “How we checked” and read the source field it names.
  3. Weigh it by kind: a signed record, a declared field, a saved prompt and a matching copy are different strengths of evidence.
  4. Remember that absence of a record is not evidence of a human author.

See the term in a real report

Frequently asked questions

What breaks a hard binding?

Any change to the hashed content: editing, cropping, recompressing, re-encoding or converting the file after it was signed.

Does a broken binding mean the image is fake?

No. It means the content changed after signing. The signature may still be valid for the original content, which this file no longer is.

Why is the manifest excluded from the hash?

So the signed manifest can be written into the file after the hash is computed; the specification defines the exclusion ranges.

How does isGenAI show a binding result?

As the cryptographic validation state in the C2PA checker and AI image detector, separate from signer trust.

Sources

Definitions follow the published standards linked above; the isGenAI behaviour described is the deployed checker as of October 2026.