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JPEG XL content provenance

Content provenanceContent provenance: The record of where a piece of content came from and how it changed, carried with the content itself. for JPEG XL files is a signed C2PA manifestC2PA manifest: The signed label itself: a small package inside a file that records who signed it, what they declared and how to check it. inside the file. Anyone can check who signed it and whether it changed, for free.

Start signing freeCheck a JPEG XL file
A file holds a signed label in four layers: who signed it, what they declared including AI use, a fingerprint of the content, and a signature that seals them together.
The label sits inside the file. It names the signer, carries what they declared, fingerprints the content, and is sealed by a signature.
File
.jxl, MIME typeMIME type: The standard name for a file format, such as image/jpeg or audio/wav, that software uses to decide how to read a file. image/jxl
Where the label sits
Inside the file, in its own top-level box, apart from the picture data.
Standard
C2PAC2PA: The Coalition for Content Provenance and Authenticity: the group that publishes the open standard for content labels., the open standard for content labels.
Made for
Modern web delivery, Photo archives, High-quality images

What Encypher supports for JPEG XL

  • SignSupported

    Encypher signs JPEG XL files under C2PA 2.2 and 2.4.

  • CheckSupported

    Free in the browser checker, with no account.

  • Formal conformanceSupported

    Covered by our C2PA 2.2 conformance record.

How to check a JPEG XL file

  1. Open the free checker.

    It runs in your browser. No account needed.

    Open the checker

  2. Add your JPEG XL file.

    Drop it in or pick it from your device.

  3. Read the result.

    It shows who signed and what they declared, such as AI use. It also shows if the file changed.

Where the label sits in a JPEG XL file

The file is made of nested boxes, a layout called ISO BMFFBMFF: ISO Base Media File Format: the box structure behind MP4, MOV, HEIF and similar files.. The label gets a box of its own.

In an MP4, MOV, HEIC or AVIF file, the label sits in its own box beside the boxes that hold the picture and sound.
A JPEG XL file keeps the label in its own top-level box, apart from the picture data.

JPEG XL is a newer image format meant to replace JPEG. It gives smaller files and can repack old JPEGs without loss.

What keeps the label on a JPEG XL file

You can add a hidden watermarkWatermark: A mark placed in the content itself, visible or hidden, so it can be found again after the file is copied. when you sign. If a copy loses its label, the watermark can lead back to the record.

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.
  • Copying, emailing and downloading the file keep the label.
  • Editing the picture after signing shows as a change.
  • Some social sites and image services rebuild the file and drop the label. Then the check finds no label.

For engineers

Show the technical detail
Embedding
JUMBF superbox (jumb) at the top level of the JPEG XL box structure
Accepted MIME types
image/jxl
Signing versions
C2PA 2.2, 2.4
Verification
Any version. The checker reads any C2PA manifest it can parse, and the report names the version it checked against.
curl -X POST https://api.encypher.com/api/v1/sign/media \
  -H "Authorization: Bearer $ENCYPHER_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -F "file=@example.jxl" \
  -F "title=My JPEG XL file" \
  -F "action=c2pa.created"

Support rows come from the live API capability matrix. Full reference: C2PA media types.

Keep reading

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