First, thank you for this wonderful program! I am currently integrating this into the Ubuntu package build process. For this I wrote a little script to verify that optipng's resulting output files are visually identical to the original files, using "convert" from imagemagick. This might be interesting for an upstream inclusion into the tarball, to provide an easy regression testing method like this:
find /usr/share/ -name '*.png' | ./optipng-check
I ran this against a few thousand files on my system.
It would be nice if you could add this to the distribution tarballs. Thanks for considering!
test script