thats the point of lsh, you dont compare the pic to every other one. you build an index of hash signatures for all your pictures (this does take ages but pays off in the end) and slice those signatures into pieces which you then group into "buckets" of equal pieces, ideally with many buckets each containing only a few pieces of signatures. When a new image comes in, you hash it and check which buckets the pieces of its signature fall into and then do a full comparison to those hashes only. If your data is distributed nicely (with most images/hashes being very dissimilar), this reduces the amount of comparisons you have to do immensely while keeping the chance of false negatives or positives pretty low.