As usual, you can get RMagick at http://rubyforge.org/projects/rmagick/
RMagick is an interface to the ImageMagick (www.imagemagick.org) and
GraphicsMagick (www.graphicsmagick.org) image processing libraries.
Supports more than 80 image formats, including GIF, JPEG, PNG. Includes
2D drawing API. Comprehensive HTML documentation.