How many ways are there to exploit the fact that visitors to your site can get the source of a pic (and video) and download it... ... the downside is that they will have no need to return, so, can you exploit this in some way that'll get them (plus several friends) to revisit!?
for example.... a subliminal messege in the video saying 'go back to the website, you loved it there'. HeHaHa, no, not really this one, but there must be ways to make these ripped visits worthwhile?
for a proper example.... watermark the pic (and video) so a bit of chosen advertising goes with it
For the subliminal message how about serving up a video with nice juicy steak in it to the veggie crowd... mmmm BEEF ...lol
Seriously I wonder if there is any legal issues surrounding that, I'm pretty sure I've heard its illegal for braodcast or the movies but that might be urban myth.
As far as the watermark goes be sure to use a good one if you really want to protect it. Static transparent ones ones are fairly easy to remove with some good success. Virtualdub has one filter I'm aware of for this and probably more. Results vary... If it's anything of importance mark it with a looping animated solid logo. The bigger the better but you may also annoy the legitimate users. Guess it depends on how far you want to take it and how valuable the video is.
Other than the watermark you could add ads in between, start middle or wherever. Other than that there isn't much you can do. The ads can easily be removed with any editor.