ImageMagick Installation

Ubuntu machine has default apt-get package manager.
To install imagemagick following packages needs to be installed.

apt-get install imagemagick librmagick-ruby libmagickwand-dev

RMagick gem install

gem install rmagick

If you still facing problems with gem installation, Please look that following packages are installed
on your system.

dpkg -l | grep libmagickcore-dev graphicsmagick-libmagick-dev-compat

If there are no packages installed then try to install then first.

apt-get install libmagickcore-dev graphicsmagick-libmagick-dev-compat

Try to install rmagick gem again. Now it should be installed without any error.