IT之家 August 26 news: Tech media NeoWin published a blog post yesterday (August 25), claiming that security researcher Xusheng Li, through reverse engineering, found that Microsoft Paint and Microsoft Photos embed a GUID identifier into AI-generated images.

IT之家 note: GUID was first reported in July this year. In a 39-page federal indictment targeting a 19-year-old hacker, it stated that Microsoft acknowledged that Windows 11 systems include a built-in Global Device Identifier (GDID), and that there is no complete option to disable it.

A global device identifier is a persistent, device-level ID Microsoft uses to recognize a particular Windows installation instance. It can be associated with an entity device or a virtual machine, and is used as a unified identification key in some Microsoft services. Typical scenarios include device catalog registration, coordination across devices for services, update distribution, and enterprise-level status reporting.

A GDID occupies 16 bytes as a 128-bit value, and in Microsoft’s Paint and Photos-related features, Microsoft servers apparently assign identifiers of this kind to prompts. Even if Copilot generates an image locally, the prompt entered by the user may still be sent to Microsoft’s servers first.

When analyzing AI features in Microsoft’s Paint application, Julia discovered the Watermarker.dll component. The drawing app already offers visible watermark options that can add a small Copilot logo to generated images; however, the researcher found that another set of hidden watermark functions operates independently of that option.

The research also states that Microsoft adds C2PA Content Credentials to AI-generated images. Xu Sheng Li found that the same watermarkId appears in the C2PA metadata as well, acting as a “soft binding” value used to link hidden watermarks in image pixels with the image’s source metadata.

Microsoft Photos also includes Watermarker.dll. The researcher found that the local Image Creator and Restyle Image features in photos also appear to embed a GUID into the generated images.