Since sha256 or whatever isn't going to cut it, I'd assume they were at least using some sort of perceptual hash concept (https://www.phash.org/ https://www.pha

Since sha256 or whatever isn't going to cut it, I'd assume they were at least using some sort of perceptual hash concept (https://www.phash.org/ https://www.phash.org/) and it's not implemented in Javascript. The system would be pretty useless otherwise if you had to report the same image multiple times for each time someone recompressed it / took a screenshot of it / a single bit was changed. The other likelihood is that they aren't just generating a hash for the same reason FaceID isn't just a hash but actually doing more interesting model-building that they only implemented server-side. Either way, it's not very great UX. But I can imagine that if you're at a place where you need to preemptively block your nudes from imminently transmitting through Facebook, you probably don't care.