I've just been reading the other post about the upload rules here and a lot has been said about slide trading there.
One thing came to my mind: What about copyright when a slide is traded. I mean there some people here (Joe, Michael) that seem to sell their slides. How can you make sure you still own the copyright of the picture. You're still the photographer but how can you prove it? So someone could buy a slide taken by a pro somewhere, scan it and upload it here. Has this ever happened to anyone? What can you do then? Is it legal?