There was an article that trended a few months back too about CC "Attribution trolls". (I can't find it in a quick search, sorry, but I can paraphrase.) There's a legal "bug" in the Attribution clauses of early CC licenses that basically says that the copyright owner gets to dictate how the Attribution must read down to detailed specifics in wording and formatting. They post to WikiCommons as CC licensed under specific old versions of CC and rely on the fact that most people don't copy and paste the attribution strings verbatim to troll for licensing fees.

(So, watch out for CC licenses older than 4.0 for that.)