There many ways to actually compare images, layer modes, difference engines and the like.
But the reason I say "Wow" is because I just tried an app that can look for and show images on your drive that are identical or similar - even if they have different filenames, pixel sizes or formats!! Voila:
The app I'm trying is:
https://www.bolidesoft.com/imagecomp...omparison.html
It is quite speedy. It searched through some 3000 images in about 3 and a half minutes. But of course there are others.
Apologies from beyond the pale if this is nothing new to anyone.