Yes, ultimately creator has the ultimate say on whether or not they feel infringed. Literary works are a different ball-game, just like the online video world, and also just like visual arts. I don't know legality details about fan-fic, music or videos, but for pictures specifically: you're clear as long as it's not trying to be stolen and sold as your own & it's modified. I've got limits to what I can do with this modified work (i.e. I can't sell it and claim I was the model or photographer) but reposting it online is well within my rights as outlined by Fair Use policy