GNU/Linux Desktop Survival Guide
by Graham Williams
ImageMagick is an excellent tool for transforming images in a multitude of ways. It is powerful and flexible, although digging into its full potential is not always easy, often requiring some research to explore how to achieve what you need. A recent book by Sohail Salehi helps in this regard--see Section 42.5.
ImageMagick is a command line tool, providing the basic commands: animate, compare, composite, conjure, convert, display, identify, import, mogrify, and montage.