The IBM developerWorks site has a new tutorial posted (registration/login required) talking about image creating in PHP using the GD library.

The purpose of this tutorial is to show you how to get started with the GD library and to provide a variety of techniques you can apply to your Web-page coding. The tutorial doesn't cover every GD function, but it teaches you the basics. The Resources section provides Web sites where you can learn more about using the GD library.

They go through the creation of sample images, working with gradients and lines, adding text, saving the image data out to a file and how to work with existing graphics to modify them.

Vinu Thomas has posted about a PHP/GD CAPTCHA solution he's come across - Secureimage.

From the company's description:

Securimage is an open-source free PHP CAPTCHA script for generating complex images and CAPTCHA codes to protect forms from spam and abuse. It can be easily added into existing forms on your website to provide protection from spam bots. It can run on most any webserver as long as you have PHP installed, and GD support within PHP.

Features of the tool include simple addition and validation methods, the ability to make audible CAPTCHAs and True Type font support. You can download the software from the project's website.