When you use the AI image tools in Windows Paint or Photos, the picture isn't as local as it looks. A researcher found Microsoft embeds an invisible watermark, a unique ID, in every AI image, and that ID can point back to you.
How it works
Security researcher Xusheng Li found that Paint and Photos send your prompt to Microsoft for "moderation," then encode the returned GUID (a 16-byte ID) invisibly into the image's pixels. It's separate from the visible "AI-generated" label you can choose to add. Because Microsoft ties each prompt to the account that sent it, the company could match a hidden ID in an image back to the person who made it. Successive prompts are even linked to each other.
Why it matters
This is the digital version of the tracking dots that color laser printers have hidden on every page for decades, the ones that alarmed privacy advocates when the EFF exposed them. An invisible, user-linked ID means a picture you thought you made privately on your own machine carries a fingerprint that leads back to you. Microsoft says it applies AI safety measures but hasn't made clear that the watermark contains a user-linked ID.
Microsoft isn't alone. Meta is building "Content Seal," and OpenAI adds Google's SynthID and C2PA data to its images.
What to do
Know where it comes from: only the built-in AI image tools in Windows Paint and Photos add this tag. The simplest fix is to not use them for anything you want to keep private. They're fine for fun, just not for sensitive images.
Assume it identifies you: the hidden ID survives cropping and resizing, so treat any image you make with these tools like a signed one, not an anonymous one.
Scrub it before sharing: remove the hidden tag, along with your location and other buried data, with a free metadata remover, ImageOptim on Mac, Scrambled Exif on Android, or on Windows just right-click the file, then Properties > Details > "Remove Properties." We go deeper on Friday.
Want a truly private option? Use an AI image app that runs entirely on your own computer, so nothing is sent off to be stamped. Free offline options exist, like Fooocus on Windows or DiffusionBee on Mac, though they take more setup than the built-in tools.
Quick tip
It isn't just AI images. Your phone stamps every photo with your exact GPS location by default. On Friday we show you how to strip that, and other hidden data, in one step on any device.
Up next · Wednesday
The single free extension that blocks most of the trackers following you around the web.