findimagedupes
find visually similar or duplicate images
Many years ago, the findimagedupes program by Rob Kudla found its way into Debian. I noticed it, played with it a bit, and filed some bug reports and suggestions for improvement. Then I forgot about it.
Some time later, I was contacted by the Debian maintainer, asking if I would submit my improvements. It seemed simpler to rewrite the code than to patch it. So, after many delays and interruptions, that's what I did.
My version of findimagedupes has now replaced Rob's in Debian and appears to be included with several other distributions.
Documentation
See the README.
Source
Latest version: findimagedupes-2.20.1.tar.gz
Originally I used RCS for revision control but I have now migrated the history into git and created a GitHub repository.
Installation
It is probably simplest just to install the version that comes with your distribution, if possible. Otherwise, you'll need Perl, GraphicsMagick, and a few CPAN modules. Read the beginning of the script for details.