Nice to see other open source CAD development being explored. BRL-CAD has had the pixdiff, bwdiff, and pixcmp tools for a very long time, for very similar purposes:

pixdiff: https://manpage.me/index.cgi?q=pixdiff&sektion=1&apropos=0&m...

bwdiff: https://manpage.me/index.cgi?q=bwdiff&sektion=1&apropos=0&ma...

pixcmp: https://manpage.me/index.cgi?apropos=0&q=pixcmp&sektion=1&ma...