ImageWorkshop is a PHP5.3+ library that helps you to manage images based on GD library
Image manipulation at it's finest.
A PHP class to handle image manipulation
An easy to use, simple to manage, web photo gallery written in PHP.
Manipulate images with an expressive API
Easily optimize images using PHP
A reliable and extensible PHP image manipulation library
Perceptual image hashing for PHP
WordPress: Manage and serve up dynamic placeholder images