I don't think I've ever clicked that button, I just type

. Well actually I have a custom bb code so I just type [qimg]filename[/qimg] because I know I will always be hosting the image in the same location so the bbcode takes care of adding all the http:// blah blah blah stuff, and even if I wanted the file extension if I wanted to limit myself to just jpg's (or gif's or whatevers).