PHP's built-in drawing primitives are like a paint program. They're great for rendering to an image, but they aren't so good if you want to think of your image as a set of objects. This article shows you how to build an object-oriented graphics library to sit on top of the PHP graphics library. You'll use the object-oriented extensions provided in PHP V5.
I lump graphics editing programs into two distinct categories: painting programs that let you tweak an image pixel by pixel and drawing programs that provide a set of objects like lines, ovals, and rectangles that you can manipulate until you render the drawing to a flat image like a JPEG.
I like that they give the structure of the app as they go right along side the code. It helps keep the focus on the object-oriented aspect of the whole script. They step you through the creation of the class, how to make a square and circle with it, how to change the z-axis, and much more...
