I agree. Call me naive, but I find it shocking how much it happens. (Even here on the bbs, so many images are posted without any credit given. Yesterday, @DeadWriter gave a three-part credit for a GIF—the source, where it was found, and where the format was converted; I felt really happy to see that, and also realized how unusual it [unfortunately] seemed.)
I suppose that as it gets easier and easier for anyone to search for images and track down sources, it will (in general) be left more and more as an exercise for the reader. Still, the social importance of giving credit where due will never go away. And the importance of being honest with ourselves about who we owe for our successes, even if posting a cool GIF is a minor success in the big scheme of things.
But if you hadn’t found it there, would you have known about it? I’d say they deserve some credit too, for having gone to the trouble to put it in front of you. (Though I’d feel reluctant about giving them credit if they didn’t credit the creator…not sure what I’d do in that case. Maybe I’d note that it was found there without attribution—which would give them some credit but also call them out for their omission.)
