Kore Nordmann has posted a new article series (to the "Articles" section of his site) with six different pieces talking about different aspects of image creation with PHP:

• Image creation with PHP - Image Tools
• Image creation with PHP - Text rendering
• Image creation with PHP - Integrating bitmaps
• Image creation with PHP - Gradient rendering
• Image creation with PHP - A first shape
• Image creation with PHP - Formats & Libraries

Each of them can be read separately, but they're all part of a series and make more sense when read together.