You're probably thinking of a perceptual hash. [0] It's a relatively new field, academically speaking, so only a few players dominate, and there is a huge amoun

You're probably thinking of a perceptual hash. [0] It's a relatively new field, academically speaking, so only a few players dominate, and there is a huge amount of research going into it. There are other techniques for automatic flagging of similar files, like PhotoDNA's [1] enormous database - which I believe PornHub are already using. [0] https://en.wikipedia.org/wiki/Perceptual_hashing https://en.wikipedia.org/wiki/Perceptual_hashing [1] https://www.microsoft.com/en-us/photodna https://www.microsoft.com/en-us/photodna