I am re-visiting this topic which was discussed nearly 3 years ago. Tweaking the template tag was mentioned, would appreciate if you can give a guide on how to do it on the latest version? Which files to edit etc...
An example of a backlinked image can be found in the above topic link.
I'm also interested in this but unfortunately I don't have the skills to put it in place. It would also complicate updates a lot.
The hotlinking is a hot (haha) topic. Remove it and users leave. Keep it and you won't get a cent from it (other than the banner when they upload). About 90% of my users are hotlinking.