paperclip_processor for watermarking that works with rails 3 and paperclip 2.3.8

watermark.rb

# from http://github.com/ng/paperclip-watermarking-app 
# with modifications from http://exviva.posterous.com/watermarking-images-with-rails-3-and-papercli
# and even more modifications to ensure works with paperclip 2.3.8 and rails 3.0.3
#
# Note: In rails 3 paperclip processors are not automatically loaded.
# You must add the following above your model class definition: 
#
# require 'paperclip_processors/watermark'

module Paperclip
  class Watermark < Processor
    # Handles watermarking of images that are uploaded.
    attr_accessor :current_geometry, :target_geometry, :format, :whiny, :convert_options, :watermark_path, :overlay, :position

    def initialize file, options = {}, attachment = nil
       super
       geometry          = options[:geometry]
       @file             = file
       @crop             = geometry[-1,1] == '#'
       @target_geometry  = Geometry.parse geometry
       @current_geometry = Geometry.from_file @file
       @convert_options  = options[:convert_options]
       @whiny            = options[:whiny].nil? ? true : options[:whiny]
       @format           = options[:format]
       @watermark_path   = options[:watermark_path]
       @position         = options[:position].nil? ? "SouthEast" : options[:position]
       @overlay          = options[:overlay].nil? ? true : false
       @current_format   = File.extname(@file.path)
       @basename         = File.basename(@file.path, @current_format)
     end

     # TODO: extend watermark

     # Returns true if the +target_geometry+ is meant to crop.
      def crop?
        @crop
      end

      # Returns true if the image is meant to make use of additional convert options.
      def convert_options?
        not @convert_options.blank?
      end

      # Performs the conversion of the +file+ into a watermark. Returns the Tempfile
      # that contains the new image.
      def make
        dst = Tempfile.new([@basename, @format].compact.join("."))
        dst.binmode
        
        command = "convert"
        params = [fromfile]
        params += transformation_command
        params << tofile(dst)
        begin
          success = Paperclip.run(command, params.flatten.compact.collect{|e| "'#{e}'"}.join(" "))
        rescue PaperclipCommandLineError
          raise PaperclipError, "There was an error resizing and cropping #{@basename}" if @whiny
        end
        
        if watermark_path
          command = "composite"
          params = %W[-gravity #{@position} #{watermark_path} #{tofile(dst)}]
          params << tofile(dst)
          begin
            success = Paperclip.run(command, params.flatten.compact.collect{|e| "'#{e}'"}.join(" "))
          rescue PaperclipCommandLineError
            raise PaperclipError, "There was an error processing the watermark for #{@basename}" if @whiny
          end
        end
        
        dst
      end

      def fromfile
        File.expand_path(@file.path)
      end

      def tofile(destination)
        File.expand_path(destination.path)
      end

      def transformation_command
        scale, crop = @current_geometry.transformation_to(@target_geometry, crop?)
        trans = %W[-resize #{scale}]
        trans += %W[-crop #{crop} +repage] if crop
        trans << convert_options if convert_options?
        trans
      end
  end
end

thanks for code