ImageMagick

ImageMagick is a collection of tools and libraries designed to read, write, and manipulate an image in many popular image formats, including GIF, JPEG, PNG, PDF, and Photo CD. With ImageMagick, you can create GIFs dynamically, making this program suitable for Web applications. You can also resize, rotate, sharpen, reduce the color of, or add special effects to, an image and save your completed work in the same or a different image format.