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I thought this might be useful to post. If you think someone ripped off/stole an image, or you might want to look at someone's reference, you can look up the image and it will show you similar images.
It also detects paintovers I think.
You have to register, but you won't get spammed or anything, it's free.
EX: Just saw this guy's thread:
And suspected a paintover, so I did a search. Found this, and it turns out it's NOT a paintover.