code: public static long totalImageDiff(BufferedImage img1, BufferedImage img2) {
  
  		int width = img1.getWidth();
  		int height = img1.getHeight();
  
  		if ((width != img2.getWidth()) || (height != img2.getHeight())) {
  			throw new IllegalArgumentException("Image dimensions do not match");
  		}
  
  		long diff = 0;
  		for (int x = 0; x < width; x++) {
  			for (int y = 0; y < height; y++) {
  				int rgb1 = img1.getRGB(x, y);
  				int rgb2 = img2.getRGB(x, y);
  				int a1 = ColorUtils.getAlpha(rgb1);
  				int r1 = ColorUtils.getRed(rgb1);
  				int g1 = ColorUtils.getGreen(rgb1);
  				int b1 = ColorUtils.getBlue(rgb1);
  				int a2 = ColorUtils.getAlpha(rgb2);
  				int r2 = ColorUtils.getRed(rgb2);
  				int g2 = ColorUtils.getGreen(rgb2);
  				int b2 = ColorUtils.getBlue(rgb2);
  				diff += Math.abs(a1 - a2);
  				diff += Math.abs(r1 - r2);
  				diff += Math.abs(g1 - g2);
  				diff += Math.abs(b1 - b2);
  			}
  		}
  
  		return diff;
  	}
docs: The total difference between two images calculated as the sum of the difference in RGB values of each pixel
  the images MUST be the same dimensions.
  
  @since 1.2
  @param img1 the first image to be compared
  @param img2 the second image to be compared
  @return the difference between the two images