There is a fourth category of hash functions: find similar items.<p>For English words, this is usually done with soundex / metaphone / doublemetaphone. Fun fact, soundex was developed over 100 years ago to help immigrants find their families in USA even if they didn't know how to spell their last name. Soundex is supported by most DBs.<p>For images, there are hashes like ahash/phash/dhash/whash/blockmeat/colormoment/colorhas/marrHildreth .<p>Most popular Audio hash is acoustid. There was also EchoPrint (with two incompatible versions), but once EchoNest was bought out by Spotify the public support and development into echoprint died. Some groups of people tried to keep echoprint alive but I am unaware if it is still used by anyone publicly.