Graphicsdiff is a git diff wrapper for artists that visualizes differences between images. It utilises imagemagick's compare and has a graphical fallback for ASCII and binary files which uses meld and hexdump.

The easiest way to use it is to overwrite the global config with
git config --global diff.external /path/to/graphicsdiff/graphicsdiff.sh

More advanced users of git can also use git-difftool [1]

Have fun :)

1 http://www.kernel.org/pub/software/scm/git/docs/git-difftool.html