imgdiff
This is a tool to compare one image file against one or more others, and create images containing the differences. Sample usage:
./imgdiff.py img1.png img{2..10}.png
This will create nine diff images named diff0.png to diff8.png. You can specify only a region of the image to be compared using the --region/-r argument:
./imgdiff.py img1.png img{2..10}.png -r 100,100,199,199
This compare the region with the top-left at (100, 100) and the bottom-left at (199, 199). Both are inclusive.
Note
If you're looking for a way to remove duplicate files in the output,
you can use the fdupes utility:
fdupes -d .