There are perceptual image hashes[0]. There even are databases that have "search by similar image" indexing[1] [0] https://www.phash.org/ https://www.phash.org

There are perceptual image hashes[0]. There even are databases that have "search by similar image" indexing[1] [0] https://www.phash.org/ https://www.phash.org/ [1] http://www.lire-project.net/ http://www.lire-project.net/