Is there such thing as a 'soft checksum' tool?

Karl Vogel vogelke+unix at
Sun Sep 6 01:21:41 UTC 2009

>> On Sat, 5 Sep 2009 10:33:03 -0600, 
>> Modulok <modulok at> said:

M> I'm looking for a pseudo-checksum tool for use with cataloging images.
M> For example, a strict checksum algorithm, like the sha family, will
M> produce a dramatically different checksum for two files which differ by
M> only a single bit.  I'm looking for something where two images, which
M> are similar, get a proportionally similar checksum.

   This works pretty well with text, but I don't know about images.
     What's a nilsimsa code?
     A nilsimsa code is something like a hash, but unlike hashes, a small
     change in the message results in a small change in the nilsimsa code.
     Such a function is called a locality-sensitive hash.

Karl Vogel                      I don't speak for the USAF or my company
Garlic gum is not funny.            --written on blackboard by Bart Simpson

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