Watermarking hotlinked images
What’s hotlinking?
“Hotlinking” is where you link to an image stored on someone else’s site without making your own local copy. It’s done a lot by people posting to forums, weblogs, or to social networking sites such as MySpace.
The usual solution to this problem is to redirect them to another (often tasteless) image indicating one’s dissatisfaction with the act of hotlinking. This is a pretty good disincentive from using other peoples' bandwidth; however, I care more about people maintaining attribution, and standard hotlink-prevention stuff simply just causes people to upload a copy of the image to another site and then keep on not attributing it; in this case it’s even worse because if someone were to look at the image’s URL, they don’t see anything regarding where the image originally came from.
One solution is to make a simple image proxy script which adds a watermark to an image, and also logs the hotlinked image.