There's no way to do it on vB. Only template edits. ^^^ Also I don't think there's a way to edit the main core files on phpBB or IPB either actually... I think you're thinking about the templates.
Yeah, I don't think there are any auto image resizing BBCodes. There's mods of course, but you'd need access to the files so you could edit them. Gotta suck to have limited access and being an Admin, but I guess I can see why VS would make it that way.
Edit:
How about this?
http://www.vbulletin.org/forum/showt...=image+resizer