    # File lib/compass/sass_extensions/sprites/sprite_methods.rb, line 84
            def uniqueness_hash
              @uniqueness_hash ||= begin
                sum = Digest::MD5.new
                sum << SPRITE_VERSION
                sum << path
                sum << layout
                images.each do |image|
                  [:relative_file, :height, :width, :repeat, :spacing, :position, :digest].each do |attr|
                    sum << image.send(attr).to_s
                  end
                end
                sum.hexdigest[0...10]
              end
              @uniqueness_hash
            end