The "?" is the problem here. BMWBoard's thread parsing scripts cannot recognize an image URL/filename with any "illegal" characters in it.. such as a question mark. You also cannot use avatars for the same reason. You have to upload the image to some other server or let TOM create another static URL.
URL you are using isn't actual location of an image. Your image is stored elsewhere on the server's database and the script acts as a middleman. Chances are this board uses ImageMagik for their image manipulation... that thing is powerfull as hell. [fake]
~P.u.S.h.