Hash by strictest definition is just a function that maps any input to fixed size output. There is a special subcategory of hashes that are locality sensitive a

Hash by strictest definition is just a function that maps any input to fixed size output. There is a special subcategory of hashes that are locality sensitive and change a little when input changes a little, just like there is a special subcategory of crypto hashes. See: https://en.wikipedia.org/wiki/Locality-sensitive_hashing https://en.wikipedia.org/wiki/Locality-sensitive_hashing Technology for searching for similar images (I have no idea how it works interally) already exists and is very widely deployed. You can easily find an image similar (uncropped, cropped, with different filter, greyed, ungreyed, with a logo in corner, etc.) to your input image on https://tineye.com/ https://tineye.com/ and https://images.google.com https://images.google.com .