Show git-diff-image output also on 'git show'  and 'git log -p'?

Is this diff tool designed to work *only*  when specifically running `git diff`, or everywhere git diffs are displayed, such as in `git log` and `git show`?

I have only gotten it working when running explicitly `git diff`. Hence I was wondering did I setup it incorrectly, or is it not being used got `git log -p`  and `gitk` output at all.