// Show a message over frozen image in the display
 public void showMessage(String message) {
   Graphics g = getGraphics();
   g.setColor(Color.black);
   g.fillRect(30, (getHeight() / 2) - 16, message.length() * 10, 25);
   g.setColor(Color.white);
   g.drawString(message, 40, getHeight() / 2);
 }