I was actually sad to find this product because I had the same idea last week and was considering actually building it, but glad to see I didn't waste my time!
I saw a tweet last week where someone was asking people to identify a logo on an image, so I cropped the photo and checked if Google's reverse image search would recognize it. It didn't, so I tried reversing the logo's color (white on black instead of black on white), and Google found the match I was looking for.
So I thought a tool like this would be handy for cases like that.
Unfortunately, Google's reverse image search doesn't seem to be "fuzzy" enough, so you sometimes get no results. But the concept is pretty awesome.
Here's an example search (I just drew a random shape and letter -- I tried Product Hunt's logo a dozen times but it wouldn't match it):
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