The basic idea is this: you have a directory with images, and want to process them with ImageMagick (because you want to resize them, or crop them, or rotate them etc.). Suppose that you have an image gallery, with a controller Photo to display the images. The image files are stored in the directory ’/var/lib/photos’. Now, if you want to generate and display thumbnails, you’d do this:

  # in the controller
  class Photo < ApplicationController
    imagemagick_for '/var/lib/photos'
  end

  # in the view
  <%= imagemagick_tag 'first_photo.jpg', 'resize(100x100)' %>

Request the view, and ta-da: the image first_photo.jpg is displayed, and it is resized to fit within 100x100 pixels. You can use many other ImageMagick commands in the same way.