I don't think any of them work on this board.
[img=50%]http://........[/img] that means: image get resized (downscaled in this case) by 50 % of its original size. Height and width will be resized automatically.
[IMG=50%]http://imageshack.com/a/img109/8748/dqiq.jpg[/img]
[img=w,500]http://.....[/img] that means: width = 500 pixels, and height will be resized automatically
[IMG=w, 480]http://imageshack.com/a/img109/8748/dqiq.jpg[/img]
[img=h,500]http://......[/img] that means: height = 500 pixels, and widtht will be resized automatically
[IMG=h,480]http://imageshack.com/a/img109/8748/dqiq.jpg[/img]
[IMG=640x480]http://imageshack.com/a/img109/8748/dqiq.jpg[/img]