[spatulan]

Or you can import the two images into graphics software like gimp. Invert the colours in the top image, then knock transparency for that layer down to 50%. If the images are identical, you'll just see grey. Any differences will instantly become visible.

[SlashmanX]

Now automate it for 200 screenshots

[yyhhsj0521]

If this is indeed the underlying algorithm it should not be hard to implement