You made a Malfoid (Female Malfoy / Fem Draco) portrait, posted it, and a week later a picture that looks a lot like it shows up on another account: smaller, maybe mirrored, maybe a screenshot with someone else's handle on top. Is it yours?

People ask assistants this all the time ("how do I check if an image is a repost of mine?"). The answer is usually "use a reverse image search", which is right but leaves out how it works and why it fails. This post builds the core idea in about 120 lines of Python (Pillow + NumPy, nothing else), tests it on twelve kinds of repost, and shows a trap specific to preset-based generators like the one I run: two different people's portraits can hash almost the same.

I build malfoidai.com , an unofficial studio that makes one still 3:4 Malfoid portrait per payment. No real portraits or faces are used below. All test images are drawn by a script.

The idea: hash what the picture looks like, not its bytes

A SHA-256 of a file changes completely if one pixel changes.…