ImageMagick

Freshmeat.net: Project details for ImageMagick
Project description, downloads, article links, and user comments.
http://freshmeat.net/projects/imagemagick/?topic_id=100

Graphics from the Command Line
Article that demonstrates that ImageMagick command line tools can be used to flip, size, rotate, and stylize various file format images in batch.
http://www-106.ibm.com/developerworks/linux/library/l-graf/

ImageMagick Hacks
A list of tools that use ImageMagick and articles that explain its use.
http://savage.net.au/ImageMagick.html