The hash functions used for these purposes are usually not cryptographic hashes. They are "perceptual hashes" that allows for approximate matches (e.g. if the i

The hash functions used for these purposes are usually not cryptographic hashes. They are "perceptual hashes" that allows for approximate matches (e.g. if the image has been scaled or brightness-adjusted). https://en.wikipedia.org/wiki/Perceptual_hashing https://en.wikipedia.org/wiki/Perceptual_hashing These hashes are not collision-resistant.