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There are specific (non-cryptographic) hashes which are built to compare equal for equal data, and to be similar for similar data (for different metrics of simi
by azernik 9y ago
There are specific (non-cryptographic) hashes which are built to compare equal for equal data, and to be similar for similar data (for different metrics of similarity). It's a somewhat esoteric subject, but it's a thing.
- Faark 9y agoThe "hash" would have to be non-reversible. When we compare images based on content, afaik we transfer them into a vector space and measure distance. Do we really have tech to make and compare such a content representation in a non-reversible way? That sounds like a lot to ask for tech that seems still in active development.
- prepend 9y agoAll hashes are non-reversible. Being one way is one of the characteristics of a hash. Depending on how effective it is, there may be collisions possible. This is kind of happened with previously common hashes like md5 where people were able to break it by generating collisions. But basically saying “as long as it is unreversable” is redundant unless you think there’s some reason to think the hash sucks.
- azernik 9y agoIf your hash is smaller than the (compressed) image itself, then you have information-theoretical loss; there is no possible way to reverse the operation. And these hashes are usually much smaller than the original.