Short answer
Not as a replacement. Machine-readable marking (paragraph 2) and human-visible disclosure (paragraph 4) are separate requirements aimed at different actors. A watermark burned into the pixels is readable by no machine — which makes it as invisible to an automated review as it is to ours.
Why that is
Paragraph 2 addresses providers of generative systems and asks for a marker in a machine-readable format. Paragraph 4 addresses deployers and asks, for deep fakes, for disclosure that the content was artificially generated or manipulated. Neither replaces the other, because they serve different ends: machine readability keeps the fact detectable further down the chain, the visible label serves the person looking at the screen. Our scanner mirrors that split — P3 inspects the bytes of the file, P5 inspects the alt text and the caption. A watermark in the pixels appears in neither. That is not a gap in our measurement; it is the point. What exists only inside the picture cannot be picked up by any automated check, including the one a competitor would run.
This is measured in check point P5 — Visible labeling of AI-generated images (Art. 50 Abs. 4).
What this means in practice
Treat the two duties separately. Machine readability comes from metadata in the file and from nothing else. Human visibility works most reliably through the alt text or the caption, because both sit in the page source and are read aloud by screen readers. A watermark can be a sensible addition but does not carry the weight alone. And label only the images that are actually affected — blanket-labelling every image would itself be an inaccurate statement.
Check it on your own page
P5 reports whether the alt text or caption carries an indication of AI generation; P3 reports the metadata. Where the metadata says AI but no visible label exists, we say exactly that. Where we find nothing at all, we say that too — that it cannot be determined from the outside whether AI images are in use.
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Legal note
This page provides general information on the EU AI Act — it is not legal advice and not a legal assessment of your individual situation (cf. German Federal Court of Justice, judgment of 9 September 2021, I ZR 113/20). It does not replace review by a lawyer. When in doubt, consult one.