What marking cannot do

Tellmark adds a signed C2PA manifest and, for images, a TrustMark watermark. Both are real, checkable technical measures. Neither is unbreakable, and neither proves anything we have not actually tested. This page says plainly what marking does not do.

A mark can be removed

A determined attacker can strip a C2PA manifest from a file, or process an image enough to weaken or destroy its watermark. Marking raises the cost of removing the evidence that a file was AI-generated. It does not make removal impossible.

The watermark survives what we tested, and nothing more

Spike S1 (28 September 2026) encoded a TrustMark Q watermark into 20 synthetic 1024×1024 test images and checked whether the watermark still decoded correctly after three specific changes:

• JPEG re-encoding at quality 75: survived on 20 of 20 images.
• Resizing to 50% and back: survived on 20 of 20 images.
• A WebP round trip: survived on 20 of 20 images.

That is the whole test. We have not measured survival after cropping, heavier compression, screenshots, other resize ratios, filters, or any combination of these, and we make no claim about them. The 20 test images were synthetic gradients, noise fields and simple renders, not real output from an image generator: treat these numbers as a starting point, not a guarantee for every image your product produces.

A mark says "made or changed by AI", nothing more

When Tellmark signs a manifest, it only ever signs the statement that a file was made or changed by AI. It never signs a statement that a file is authentic, unaltered or human-made. The absence of a mark proves nothing either way: a file with no Tellmark mark could still be AI-generated by a different tool, generated before marking was integrated, or run through a service that strips marks.

The checker reports marks, not a verdict on the file

The free checker and the verify page report which C2PA manifest and which watermark, if any, a file carries. They do not decide whether a file is AI-generated. A file with no detected mark has not been shown to be human-made, and a file carrying another vendor's mark is reported as exactly that, another vendor's mark, not independently checked against that vendor's own records.

The signing certificate is not yet on the official trust list

Tellmark currently signs with its own certificate, which is not yet on the C2PA trust list. Until it is, a validator reports the manifest as validly signed, but by a signer it does not recognise, rather than by a certificate authority on the official C2PA trust list.

Describes technical measures. Not a legal assessment.