phpThumb() - The PHP thumbnail generator

For those developers that need PHP automated manipulation of images: crop, resizing, thumb, watermark and cache of all of it...

phpThumb() uses the GD library to create thumbnails from images (JPEG, PNG, GIF, BMP, etc) on the fly. The output size is configurable (can be larger or smaller than the source), and the source may be the entire image or only a portion of the original image. True color and resampling is used if GD v2.0+ is available, otherwise paletted-color and nearest-neighbour resizing is used. ImageMagick is used wherever possible for speed. Basic functionality is available even if GD functions are not installed (as long as ImageMagick is installed).

http://phpthumb.sourceforge.net/ - Demo and download page.