static BufferedImage addRandomSizedBorder(BufferedImage img) {
  int top = random(20), bottom = random(20), left = random(20), right = random(20);
  int w = img.getWidth(), h = img.getHeight();
  BufferedImage img2 = createBufferedImage(left+w+right, top+h+bottom, Color.white);
  Graphics2D g = img2.createGraphics();
  g.drawImage(img, left, top, null);
  g.dispose();
  ret img2;
}