[img_scale/] resizes an input image proportionally to some percent of it’s original dimensions. The value should be a positive integer; percent="100" is fullsize; percent="50" is halfsize; etc.
[img_scale output="{format}" percent="{int}"]<source>[/img_scale]percent
[img_scale output="img" percent="50"]atest.gif[/img_scale]
<img src="/wp-content/uploads/image-cache/1d2cf16c/atest_gif/scale_50.gif" width="86" height="121" alt="atest.gif" />
[img_scale output="img" percent="200"]atest.gif[/img_scale]
<img src="/wp-content/uploads/image-cache/1d2cf16c/atest_gif/scale_200.gif" width="344" height="486" alt="atest.gif" />