What exactly should be supported - simply displaying an image left and the other right?
That would be a good first step. But you can also get more advanced like slides, or like imagemagick
GitHub has quite powerful image diff possibilities: https://github.com/blog/817-behold-image-view-modes
They are very useful in practice, so something like this would be amazing. The different modes allow to chose the diff that shows the changes the best for the given changes.
Displaying images on the left/right would be great! In addition to the image diff, it would be helpful to see some metadata like filesize and image size (in pixels).
A slider for the image diff would be cool, but not very important. Currently you don't see anything when changing an image, so just displaying old and new images side by side would already be a huge improvement ;)
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