How do I mark AI images in a machine-readable way?

Short answer

Through metadata inside the image file: a C2PA manifest (Content Credentials) and/or the IPTC "Digital Source Type" field carrying a value that indicates algorithmic origin. Both live in the file rather than in your HTML — and both are easily destroyed by resizing.

Why that is

Paragraph 2 requires outputs to be marked in a machine-readable format and detectable as artificially generated or manipulated. Two mechanisms have become standard. C2PA (Content Credentials) stores a signed manifest inside the file container — a dedicated segment in JPEG, a dedicated chunk in PNG. IPTC/XMP carries the field "Iptc4xmpExt:DigitalSourceType" with values such as "trainedAlgorithmicMedia". Our check P3 looks for exactly those, as a byte-level analysis of the image file actually served: no language model, no estimate, nothing about the picture content. Either the markers are in the file or they are not. That is why this point is not arguable — anyone can recompute it.

This is measured in check point P3 — Machine-readable labeling of images (Art. 50 Abs. 2).

What this means in practice

Export images from the generating tool in a way that writes the marker, and keep that original file. Then test every processing step on its own — cropping, resizing, upload into the CMS, delivery through a CDN — instead of assuming the data survives. The failure is rarely at generation; it is in the chain afterwards, where many image optimisers write a fresh file without metadata and the label disappears before the image ever goes live.

Check it on your own page

P3 fetches the images embedded on your page and reports, per image, whether C2PA data is present and which DigitalSourceType it carries. That tells you on real files whether your pipeline preserves the marker — the part that actually fails in practice.

Related questions

• Is a visible watermark enough to meet the labeling requirement?
• What has applied since 2 August 2026 — and for whom is 2 December 2026 a transition deadline?
• How do I document that my website meets the requirements?