static BufferedImage rotateImageClockwise90(BufferedImage img) {
  int w = img.getWidth(), h = img.getHeight();
  BufferedImage canvas = newBufferedImage(h, w);
  Graphics2D g = canvas.createGraphics();
  g.translate((h - w) / 2, (h - w) / 2);
  g.rotate(Math.PI / 2, h / 2, w / 2);
  g.drawRenderedImage(img, null);
  ret canvas;
}