Cropping images with paperclip

cropper.rb

# lib/paperclip_processors/cropper.rb
module Paperclip
  class Cropper < Thumbnail
    def transformation_command
      if crop_command
        puts "CROP: #{crop_command + super.join(' ').sub(/ -crop \S+/, '').split(' ')}"
        crop_command + super.join(' ').sub(/ -crop \S+/, '').split(' ')
      else
        super
      end
    end

    def crop_command
      target = @attachment.instance
      if target.cropping?
        ["-crop", "#{target.crop_width}x#{target.crop_height}+#{target.crop_x}+#{target.crop_y}"]
      end
    end
  end
end

user_photo.rb

    # Model with has_attached_file

    # Logo managed by the Paperclip plugin
    # http://tim-stanley.com/post/standard-web-digital-image-sizes/
    has_attached_file :photo,
      :styles => {
        :medium => "240x160>",
        :small  => "100x100>",
        :thumb  => {:geometry => "50x50>", :processors => [:cropper]}
      }

    validates_attachment_content_type :photo,
      :content_type => ["image/png", "image/gif", "image/jpg", "image/jpeg", "image/bmp", "image/tiff"],
      :message => "Acceptable image file formats are .png, .bmp, .tiff, .jpg and .gif"
    validates_attachment_size :photo, :in => 1..2.megabytes,
      :message => "Please choose a smaller image. Maximum file size is 2 MB"

    after_create :reprocess_photo, :if => :cropping?

    def cropping?
      !self.crop_x.blank? && !self.crop_y.blank? && !self.crop_width.blank? && !self.crop_height.blank?
    end

    private
    def reprocess_photo
      photo.reprocess!
    end