sbool bwImagesIdentical(BWImage img1, BWImage img2) {
  if (img1 == img2) true;
  if (img1 == null) ret img2 == null;
  if (img2 == null) false;
  
  int w = img1.getWidth(), h = img1.getHeight();
  if (w != img2.getWidth() || h != img2.getHeight()) false;
  
  byte[] pixels1 = img1.pixels, pixels2 = img2.pixels;
  ret Arrays.equals(pixels1, pixels2);
}