Install RMagick

1. grab the ImageMagick.tar.gz:
   wget ftp://ftp.imagemagick.org/pub/ImageMagick/ImageMagick.tar.gz
2. Unarchive it:
   tar xvzf ImageMagick.tar.gz
3. install ImageMagick
   cd ImageMagick-6.3.8 "Or whichever the current version is, of course."
   ./configure
   make (wait~~~)
   sudo make install
4. download rmagick-2.2.2.gem:
   wget http://files.rubyforge.mmmultiworks.com/rmagick/rmagick-2.2.2.gem
5. install rmagick:
   sudo gem install rmagick-2.2.2.gem
6. (see http://rmagick.rubyforge.org/install-faq.html, search "libMagickWand.so.1"):
   add this line "export LD_LIBRARY_PATH=/usr/local/lib" to ~/.bashrc
7. test
   ruby -rubygems -e "require 'RMagick'; puts Magick::Long_version;"
   irb -rubygems -r RMagick

ref: http://zzhang.javaeye.com/blog/162994