Microsoft Paint and Photos Embed Server-Issued GUIDs as Invisible Watermarks in Locally-Generated Images
MS Paint and Photos inivisibly watermark even locally generated output with GUID
Reverse engineering reveals that Microsoft Paint and Photos, despite generating images locally on Copilot+ PCs, send prompts to a remote moderation server that returns a GUID. This GUID is then invisibly watermarked into the image pixels via a custom algorithm in Watermarker.dll, independent of the visible watermark setting. The same GUID appears in C2PA metadata, linking the content to its provenance even if metadata is stripped.
In other words, 'generated locally' does not mean that the complete operation is local. Microsoft receives and moderates the prompt, then issues the unique GUID that Paint embeds into the locally generated image.