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

[Charlie Kester]

On Sat 05 Sep 2009 at 09:33:03 PDT Modulok wrote:
>List,
>
>I'm not even sure such a tool exists, but it's worth asking:
>
>I'm looking for a pseudo-checksum tool for use with catalogging
>images. For example, a strict checksum algorithm, like the sha family,
>will produce a dramatically different checksum for two files which
>differ by only a single bit. I'm looking for something where two
>images images, which are similar, get a proportionally similar
>checksum. When I speak of similarities I'm referring to their image
>patterns. i.e two images of differing sizes, which are otherwise
>identical, would produce very similar checksums. So the closer the
>checksums are, the more similar two given images are.
>
>Does anyone know of anything like this?

libpuzzle might be what you're looking for.  There's a tool called ftwin
that uses libpuzzle to find duplicate or only-slightly-modified files.

http://libpuzzle.pureftpd.org/project/libpuzzle
http://jok.is-a-geek.net/ftwin.php

Both of these are in the portstree.  ;-)