GitHub offers 3 ways for you to diff your images. For example, this commit diff shows how I checked in an image and then changed the image completely in the next commit.
At the bottom of the image, you’ll see the options for 2-up, Swipe, and Onion Skin.
The default view is the 2-up, which shows the images before and after side-by-side.
Swipe allows you to do more of a pixel-by-pixel comparison by allowing you to slide a splitter back and forth over the image.
Onion skin allows you to pick up on subtle changes you might have otherwise missed. Although there’s nothing subtle with the image I picked