domm pointed me to
Imager - Perl extension for Generating 24 bit Images
definitely also worth a try.
the main advantage over imagemagick and gd is that it doesn't need any additional programs installed to run (just libpng, libjpeg and libungif). compiling imagemagick on a distribution without Xfree-RPM (like trustix linux can be a pain in the ass, since it needs lots of X-headers ...