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Content provenance verification

A provenanceContent provenance: The record of where a piece of content came from and how it changed, carried with the content itself. check reads the signed label in a file or text and gives one of five results. It tells you who signed, what they declared, and whether the content changed. It never says the content is true.

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Four of the five answers a provenance check can give: Verified, Modified after signing, Issuer not recognized, and No provenance found. The fifth is Could not verify.
A check reports who signed and whether the content changed. It never says whether the content is true.
Cost
Free in the public checker. No account.
Formats
79 file and media formats, including plain text.
One check
C2PAC2PA: The Coalition for Content Provenance and Authenticity: the group that publishes the open standard for content labels. labels, supported watermarksWatermark: A mark placed in the content itself, visible or hidden, so it can be found again after the file is copied. and recovery, each reported on its own.
Repeatable
Open-source libraries can repeat the same check without us.

The five results a check can give

The checker shows exactly these words.

Each result, what it means, and what to do next.
ResultWhat it meansWhat to do
VerifiedSigned by a C2PA-trusted issuer. Provenance is intact.Rely on who signed it. Read what they declared, including any AI use.
Valid signature, issuer not recognizedProvenance is present and intact. This issuer is not on the C2PA Trust List.The file is intact, but the signer is not on the list checkers trust. Decide if you know them.
Modified after signingThis provenance does not match the current file.Someone changed the content after it was signed. Ask the sender for the original.
Could not verifyThe signature could not be validated.The signature is broken or malformed. Treat the label as missing.
No provenance foundThis file has no embedded provenance.No label in this copy. It may never have had one, or a site stripped it.

What a check looks at

A checker trusts a signature when the signer's certificate was issued by a certificate authority on the C2PA Trust List, and trusts the timestamp when it comes from an authority on the C2PA TSA Trust List. The Conforming Products List shows the signing tool was tested.
Trust is about who signed and when. It does not make the content true.

  1. Find the label.

    It reads the label from inside the file, or from the hidden characters in text.

  2. Check the signature.

    It checks the digital signatureDigital signature: Math that shows which key signed something and that it has not changed since. Any edit to the signed bytes breaks it. and whether the signer is on the C2PA Trust ListC2PA Trust List: The list of signing authorities that conforming C2PA checkers trust by default..

  3. Compare the content.

    It takes a fresh hashHash: A short fingerprint of exact bytes. Any change, even one character, gives a completely different hash., a short code worked out from the content, and compares it with the signed one.

Beyond the label in the file

One check, in the free tool or through the APIAPI: Application programming interface: a way for one program to ask another to do a job, such as sign a file., covers more than the label. Each kind of evidence keeps its own line in the result.

Hard binding is a fingerprint of the exact file, so a re-encode breaks it. Soft binding is a watermark in the picture that still leads back to the label after a re-encode.
The fingerprint proves the file is unchanged. The watermark finds the label again when the file has changed or lost it.
Watermarks
Supported text, image, audio and video marks report what was found and the limits it was tested under.
Recovery
If the label was stripped, a supported mark can lead back to the signed record. How recovery works
Your policy
Your own rules run on the evidence. They never replace the result with one vague flag.

Checking a quote from an article

For text Encypher signed sentence by sentence, a quote checkQuote integrity verification: Checking that a quoted passage, for example in an AI answer, matches the signed original word for word. confirms a single sentence. It says whether that sentence appears, unchanged, in the signed article. An AI tool can run it before it quotes a source.

Questions

Is checking free, and do I need an account?
Yes, it is free, and no. Anyone can check a file or text in the public checker. Production use through the API, with your own policy and volume, is a paid service.
Does a Verified result mean the content is true?
No. It means a signer the checkers trust signed it and nothing changed since. Whether the content is accurate is a separate question.
Can a check confirm one sentence from an article?
Yes, for text Encypher signed sentence by sentence. Submit the sentence and the check says whether it appears, unchanged, in the signed article.
Does checking need the internet?
No, not for the basic check. Open-source C2PA libraries check a file on your own machine. Only the optional check for revoked certificates goes online.

For engineers

Show the technical detail

How C2PA validation runs

The endpoint detects the media type and the checks that apply. It extracts the JUMBF manifest store (an APP11 segment in JPEG, a caBX chunk in PNG, a uuid box in ISO BMFF) or, for text, decodes it from the invisible Unicode characters in the text. The manifest is CBOR. The COSE signature is validated against the signer's X.509 certificate chain up to a root on the C2PA Trust List, with optional OCSP revocation checks. The hard-binding hash is then recomputed over the asset and compared. Verification is version-agnostic and the report states the spec version it validated under.

Public check
POST /api/v1/public/verify (text) and /api/v1/public/verify/media (files), no key.
Open source
c2pa-rs, with c2pa-python and c2pa-js built on it, verify manifests locally.
Conformance
All 79 verifiable formats are checked at the endpoint. 20 media types are in our formal C2PA conformance record, a narrower measure.
Sentence checks
A quote check returns the sentence and its position in the signed article.

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