phpThumb() is the PHP thumbnail generator library that handles all the hard work on creating thumbnails with only few lines of code.
It accepts any source types for images (from the filesystem, URL or database) and all popular image formats.
PHP library have many image processing options (blur, sharpen, colorize, saturation, gamma, etc) and support for many input image formats across all versions of GD, including JPEG, PNG, GIF and BMP (even without ImageMagick)
Images can be rotated, cropped, watermarked, their quality can be defined and there is even a built-in caching to minimize the server load.
Requirements: PHP 4.0.6+ and GD library