Like Van says, ImageMagick does not seem to be installed on most hosts. (I have seen a few that has though, but only in Norway).
If you have a good reason for not using GD (such as expecting bitmap images), you may want to try ImageMagick or netpbm. In many cases, you can actually install this software yourself. It does not necessarily require system administrator to do so. Check the IM/netpbm docs for more info (I have never tried installing as anything but root, but it should, theoretically, be doable). You will need a host that allows you shell-access though.
Anyway, GD is probably the best choiche if it does what you need.