For images, watermarking.. something like what Ashoka Arts is doing is good,
www.ashokaarts.com
What ever method is used to capture the image, the watermark will remain. As users, you can still see the image properly. But if the image is used elsewhere the source would be known. Of course you can do a digital clean-up of the image, but it will be time consuming and traces of the watermark can still be found..