Microsoft embeds user-linked invisible watermarks in AI images generated by Paint and Photos
A researcher discovered that Microsoft’s Paint and Photos apps add an unseen GUID to AI-generated images, which can be tied back to the user’s prompt.
Researcher Xusheng Li, a software developer at Vector 35, published a technical breakdown of how Microsoft’s Paint and Photos applications watermark AI-generated pictures. When a user submits a prompt, Microsoft’s backend moderates it and returns a globally unique identifier (GUID), which the apps invisibly encode into the image pixels. The GUID, a 16-byte integer, is stored in the C2PA metadata manifest and can be correlated with the user’s account, effectively linking the image to its creator.
Li notes that this method differs from the optional visible watermark offered in Microsoft 365 AI tools. While Microsoft has announced compliance with EU AI transparency rules, it has not explained the presence of the user-linked GUID. The company declined to comment when approached for clarification. Similar watermarking efforts are being pursued by Meta and OpenAI, prompting privacy-concerned users to consider on-device or open-source alternatives.
Why it matters
The hidden identifier could allow Microsoft to trace AI-generated images back to individual users, raising privacy concerns.
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