I remember from way back a when there used to be some scripting that would the discourage the browser from allowing it.
But it was easily defeated by disallowing script.
Only options are really watermarking, or digimarking.
The latter is a service your paying for. They look for your image to show up somewhere else on the web.
Then you need to try and get it removed. Essentially you SOL if its outside of the US.