I assume with the 'popularity' bias (probably not the right phrase) in the modern internet this is pretty much the future of search. Someone comes up with something cool, posts a pix, and someone else puts it on Twit/Face/Tube/whatever and it gets reposted over and over and over and since the original is some worthless peon as far as the algorithm is concerned you'll never, ever find them.

From my experience it’s only because many times the original copy is gone. Without Pinterest, you wouldn’t even find it anymore.

And even if you are logged in, good chances you get redirected to some other useless page rather than the image you were trying to view. Or if you're not logged in, by the time you do get logged back in, you lose the original link and you're dumped on a random feed.