Came across this on Pro Git 7.2 Customizing Git Git Attributes

You can use git attributes to allow for customized diff of binary files.

My current additions to my global git config are

git config --global diff.strings.textconv strings
git config --global diff.exif.textconv exiftool

Then in projects (either .gitattributes or .git/info/attributes depending on whether you want it checked in or not):

*.<ext> diff = <diffname>

For example

*.png diff = exif
*.jpg diff = exif
*.doc diff = strings