This is a compact (one-file only), lightweight, object-oriented image manipulation library written in and for PHP, that provides methods for performing several types of image manipulation operations. It doesn't require any external libraries other than the GD2 extension (with which PHP usually comes pre-compiled with).
With this library you can rescale, flip, rotate, crop and sharpen images. It supports loading and saving images in the GIF, JPEG and PNG formats and preserves transparency for GIF, PNG and PNG24.
The cool thing about it is that it can re-size images to exact given width and height and still maintain aspect ratio!
Zebra_Image's code is heavily commented and generates no warnings/errors/notices when PHP's error reporting level is set to E_ALL.