fannish etiquette question

With the proliferation of Tumblr, what do you do if another fan just reblogs your pictures? I understand that one of the reasons people like Tumblr is because it is so easy to just post a bunch of pictures and video and such, but I do have a notice that I don't want my art distributed without permission, because I'd rather like traffic to come to my site than some random Tumblr or other site. (This seems to be an ongoing problem for me of late.) Am I just behind on the new fannish normal?