Your 'local' AI image asks a Microsoft server for permission first — and comes back stamped with an ID only that server can read
A reverse-engineering write-up published on 20 August, and widely picked over by developers this week, traces what happens when Paint's Cocreator or Photos' Image Creator generate a picture on a Copilot+ PC. The prompt goes first to a remote Microsoft moderation endpoint, which returns a revised prompt, a generation ID and a 16-byte GUID. The NPU then makes the image locally, and Watermarker.dll embeds that GUID invisibly into the pixels using a content-adaptive block technique. The same identifier is written into the file's C2PA Content Credentials as a soft binding. It applies only to AI-generated output — images you merely edit are untouched.
Why it mattersThe pixel watermark survives things metadata does not: screenshots, re-encoding, stripping the file's headers. That is the point of soft binding, and for tracing deepfakes it is a feature. The part worth knowing is the other half: the identifier is issued by a server that saw your prompt, so every image carries a token linking it back to that session. 'Generated locally on your device' turns out to describe where the compute happened, not where the record lives.
▶ Related video: What Is C2PA Metadata? The Future of AI Image Verification & Content Authenticity
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