gistfile1.rb

class Photo < ActiveRecord::Base
  belongs_to :gallery
  has_attached_file :image, 
		     :styles => { :large => "640x480>",
		     :medium => "150x150#",
		     :thumb => "75x75#" }
		                                 
  validates_attachment_presence :image
  validates_attachment_content_type :image,
                                    :content_type => ['image/jpeg', 'image/jpg']
end