That makes sense - if they were using a cryptographic hash then people could get around it by making tiny changes to the file. I’ve used some reverse image search tools, which use perceptual hashing under the hood, to find the original source for art that gets shared without attribution (saucenao pretty solid). They’re good, but they definitely have false positives.

Now you’ve got me interested in what’s going on under the hood, lol. It’s probably like any other statistical model: you can decrease your false negatives (images people have cropped or added watermarks/text to), but at the cost of increased false positives.