Yeah, that's what gets me most. Everyone is expected to be really careful with every snippet of text and giving all sources or it's "plagiarism" and of course full archiving is a big no-no, but with images all is fair game.

In my more cynical moments I think especially with the sourcing (which at least this Tumblr did, which isn't even the norm, I would have never noticed if it hadn't) it's because you can search for text, but the chances to find out where an image came from if it isn't sourced is pretty much nil.