// Note: This can probably be optimized if all pixels are direct-grabbed
// and image2 is expendable (then you can use it as output?)
static BufferedImage imageChangeOverlay(BufferedImage image1, BufferedImage image2) {
  assertSameSize(image1, image2);
  int w = image1.getWidth(), h = image1.getHeight(), n = w*h;
  int[] pixels1 = pixelsOfBufferedImage(image1);
  int[] pixels2 = pixelsOfBufferedImage(image2);
  int[] pixelsOut = new[n];
  for i to n: {
    int rgb = pixels1[i];
    pixelsOut[i] = rgb == pixels2[i] ? 0 : rgb;
  }
  ret newBufferedImage(w, h, pixelsOut);
}