Limiting the usage of dynamic URLs in IMG tags?

[Liorchen]

I want to enable Dynamic URL for IMG tags in my forum so my users would be able to use an image rotator script that is located on the server, but I understand it's a security breach to have it on. Is there a way to limit the usage of dynamic URLs to local server only? or furthermore, even just to a specific URL/script. Or maybe there's a better way to shield it up?