Even though my site is for registered...
 

Even though my site is for registered members only. And you can't see the photo's unless they register. Can they post the link to the picture or file and someoneelsecan download it at another site, therefore using my bandwidth? Thanks

If someone posts a link on your forum then the file can be downloaded but you can prevent filelinking on other sites by htaccess

You can find tips on how to set that up here to prevent hotlinking

http://www.photopost.com/tipsphp.html

Thank you Omegatron. After further investigations on this topic, I found out my host plan included a hotlink protection :D program! So I'm using it!