humet,
Resizing images with GD is a CPU intensive activity. I am not sure if this script is resizing images with each request or not, however, if it is, I can easily see why your host would ban it.
One solution is to resize the images once (probably when they're uploaded to the server), and store those resized images as static files (.gif or .jpg). At that point, it becomes a trivial matter to serve them up to the requestor.
It looks like this script already supports the notion of a manually generated thumbnail. I would investigate this option and pretend that GD is not even installed on your server. This should dramatically decrease your CPU usage.
Linear Mode
