install ImageMagick (yum install ImageMagick), then something like this: $ compare aaa.png bbb.png -highlight-color violet \ -lowlight-color darkgray -compose threshold jpg:- \ | convert jpg:- -fuzz 2% -fill red -opaque '#915e99' \ png:cmp-aaa-bbb.png will generate cmp-aaa-bbb.png effectively diffing bbb.png against aaa.png NB: see also img-diff in dotfiles.git/.bashrc