Single post in A Somewhat Extensive Guide to BBCodes

Is there a way I can set a size in the img tag itself? Looking around the internet it looks as though the code should be [ img=150x150]URL[ /img] or [ img width="100" height="50"]URL[ /img] the first one makes no difference and the second one gives an error. Just thinking that this would be easier than having to use styleclasses for certain images in a post

[css=height: (number)px; width: (number)px][img]image url here[/img][/css]