In the interest of full disclosure, I have identified a couple of mystery paintings using Google Reverse Image Search. But in each case there were other versions of the same painting on the net.
I typically use Google Image to ID relics on this forum. The trick is discovering the identifying terms used by the unknown person who posted a similar object. More generic terms bring more results which requires more "eyeballing" and I simply don't have time to scroll through so many possibilities. More specific terms rarely bring viable results. I've learned through experience which terms seem to work best. Still, it is often tedious and frustrating.