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

Michaël Grünewald michaelgrunewald at
Tue Sep 8 09:34:33 UTC 2009

perryh at wrote:
> Mel Flynn <mel.flynn+fbsd.questions at> wrote:
> However, thinking about this inquiry and JPEG in the same sentence
> has given me an idea that might help the OP:  JPEG is a "lossy"
> compression, with the degree of loss related to the chosen image
> quality, so two "similar" images might become identical -- or at
> least more similar -- if compressed to a sufficiently low quality
> using the JPEG algorithm.

This seems to be an excellent idea. A similar approach can 
(successfully) be used to let a computer recognize songs through a 
micrOphone: the incoming signal is transformmed to MP3 at a rather low 
quality, which provides a sort of fingerprint of the input. The quality 
factors shall be adujsted adequately for this application: there is a 
tradeoff between stability (noise insensitivity) and separation to find.

The case of images is much more complicated if one wishes to recognize 
the same image at two different scales.

More information about the freebsd-questions mailing list