Syntax for image resizing?

I've been wondering about the code this forum uses. I specifically tried two standard BBCode syntaxes for it:
[img width={width} height={height} ...]{url}[/img]
...and...
[img={width}x{height}]{url}[/img]
But neither seem to work. Maybe I'm just messing it up somehow... What is the right syntax for showing an image resized?
[img width={width} height={height} ...]{url}[/img]
...and...
[img={width}x{height}]{url}[/img]
But neither seem to work. Maybe I'm just messing it up somehow... What is the right syntax for showing an image resized?