ImageMagick
On Debian and Ubuntu, a simple
#> aptitude install imagemagick
All instructions for installation are on ImageMagick website. Howto for ImageMagick installation
Once ImageMagick has been added to your PATH, you can test it has been correctly installed, by doing::
$> convert --version
You may have to install GhostScript and FootMatic in addition to ImageMagick. You can download binaries for Mac OS X here : http://www.linuxfoundation.org/collaborate/workgroups/openprinting/macosx/foomatic