Getting to know GD

in PHP added by Sidewinder, on 9/11/2007 beginner tutorials gd general

Have you ever been on aim and received a message from one of your friends with a big long URL followed by something like John%20Is%20Stupid; You know what ever it is, wont be worth your time, but you click on it anyway to find someone goofy looking holding a sign and on it printed in big bold letters "John Is Stupid". Ever wonder how they work?