RMagic安装手记：
$ sudo apt-get install imagemagick
$ sudo gem install rmagick --include-dependencies
出现“configure: error: Can't install RMagick. Can't find Magick-config or GraphicsMagick-config program.” 错误。按提示安装以下包：
$ sudo apt-get install libmagick9-dev
再次安装gem：
$ sudo gem install rmagick --include-dependencies
重启Rails服务，RMagic安装成功。
require 'rubygems'
require 'RMagick'
img = Magick::Image.read(’logo.jpg’).first
width,height = 50,50
thumb = img.resize(width,height)
thumb.write(’my1.jpg’)