Pinterest (re)hosts the images so I'm not sure what you're suggesting. That Google write custom logic that supposedly unrolls this indirection on this one site where the image sources already exist on other sites?
I find that hard to believe considering the resources they’ve put into Content ID at YouTube for copyright infringement identification and takedowns.
But well put: If google wants to pretend it is quality material because it sits on a giant content farm they should indeed credit the original source for it. If they cant find it it should not be listed.
If it was text the entire content farm would be erased from the index indefinitely.