I can't seem to get this down to a single command with ImageMagick, but this should produce the desired result: compare key.png messageXORkey.png -compose sr

I can't seem to get this down to a single command with ImageMagick, but this should produce the desired result: compare key.png messageXORkey.png -compose src -highlight-color black message.png convert diff.png -negate message.png Though this solution will only really work for black and white images.