def diff_iterator
      @images.first.height.times do |y|
        @images.first.row(y).each_with_index do |pixel, x|
          unless pixel == @images.last[x,y]
            @diff_index << [x,y] 
            pixel_difference_filter(pixel, x, y)
          end
        end
      end
    end
def diff_iterator
      @images.first.height.times do |y|
        @images.first.row(y).each_with_index do |pixel, x|
          unless pixel == @images.last[x,y]
            @diff_index << [x,y] 
            pixel_difference_filter(pixel, x, y)
          end
        end
      end
    end
Run through all of the pixels on both org image, and fresh image. Change the pixel color accordingly.