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

Lowell Gilbert freebsd-questions-local at
Sun Sep 6 17:34:25 UTC 2009

Modulok <modulok at> writes:

> 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?

It turns out this is a remarkably hard problem.

You can look at p5-Image-Compare, but be prepared to experiment before
trusting the results.

Lowell Gilbert, embedded/networking software engineer, Boston area

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