PHP Image Manipulation Library – Zebra_Image
Zebra_Image is an open source and lightweight image manipulation library built with PHP.
The library is object-oriented, requires only the PHP GD2 extension and supports resize, crop, rotate and flip operations.
It works with .JPG, .GIF + .PNG formats and can convert one format to another after each action (transparency is preserved as well).
For the most-used function, image resizing, there are various methods offered for a smart resize like "keeping the aspect ratio", "resizing with prioritizing width or height" and "resizing by cropping".
It is also possible to define the quality of .JPG outputs.