XF 1.4 Only allowing signature pictures to be hosted on selected server

Hi guys ,
Recently we had a freak out on the forums because a guy had a signature with a picture link from
s7(dot)directupload.net , As some may know Chrome is flagging the website because it was hacked or something , So i was wonder if it would be possible to only allow users to upload small images to a selected server only and block others , Also i used censoring for *s7(dot)directupload.net* , would that work for pictures and signatures ?.