Here is some info on the tage:
[R] = Redirect the request to a new file. In this case it is going to return the hotlink.jpg
[L] = Stops the Rewrite process
[F] = Returns a Forbidden code 403, thus the little "x" from anyone trying to leach.
[NC] = no case
[OR] = switches to the next Rewrite Condition
Here is a detailed document for the other options:
http://docs.rinet.ru/CP7/ch12.htm
Hope this helps.