A software developer has reported that Microsoft embeds a server‑issued globally unique identifier in images produced by Paint and Photos, tying each image to the prompt that created it and to the user who submitted the request. The European Union’s AI transparency code of practice obliges participating companies to attach machine‑readable metadata that indicates whether content was created with AI, but it does not prescribe a specific technique. Li, a developer at Vector 35, explained that the identifier is a 16‑byte integer stored as an invisible watermark in the image pixels. Microsoft sends each prompt to its servers for moderation, receives the GUID, and records the previous prompt generation ID to link successive requests. The GUID can therefore be used to associate an image with a specific user. Meta is developing a watermarking system called Content Seal, and OpenAI applies Google DeepMind’s SynthID and C2PA metadata to its images, indicating broader industry movement toward mandatory tracking. Critics note that the approach mirrors earlier printer tracking methods that raised privacy alarms. Users who wish to avoid embedded identifiers may run open‑weight models such as Stable Diffusion on their own devices. The balance between compliance with EU regulations and user privacy remains unresolved as Microsoft has not responded to requests for comment.