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5 stars.

This is the best utility to detect if your image has been transmogrified.

You can also use ImageMagick to generate a "diff" image:

magick compare img1.jpg img2.jpg diff.jpg

If you want a numeric result, you can use "-metric AE" (and a null output file) to count the number of pixels that differ.

There is also a "fuzz" option: -fuzz 2%

I think he's referencing to the Calvin and Hobbes Transmogrifier. The name of the util reminds of one of the personalities of Calvin : Spaceman Spiff