While my hat is off to Apple for making PHP installed by default on the Mac, it is kind of amazing that they did not include support for the GD package at all. No matter, you can install the PHP GD package on the Mac using 7 simple steps as described here http://www.maltete.com/blog/index.php?2008/05/03/388-installing-php-with-gd-library-working-on-mac-osx-105-leopard. I went through this process myself and it worked perfectly. Aside from the download, it's very quick. And the nice thing is it's reversible too (just remove the symbolic link and remove the one edited from httpd.conf) so if it does interact in some way with a package you already have installed, you don't end up stuck in an even worse state.