Jacek Artymiak published the second edition of his "Dynamic Bitmap Graphics with PHP and GD" tutorial over on DevGuide.net today focusing specifically on creating bitmaps on the fly.

The 39 page guide ($15 USD from Lulu.com) provides a wealth of knowledge about working with graphics in PHP including a detailed look at some of the more advanced functionality of GD. The book covers your first steps with GD and graphics, working with primitives, creating an image based on external data, and embedding them into an XHTML/HTML page of your choosing.

The page for the book on DevGuide.net itself even provides a great list of resources for those looking to get into graphics with PHP - with links to everything from the basic software (webservers, PHP, etc) out to the libraries you'll need and some other tutorials to help you even after you've worked through the book.