function swapImage(imgId) {
  current_img = document.getElementById(imgId);
  if (current_img.src.indexOf("-rot") > -1) {
	current_img.src = current_img.src.substring(0, current_img.src.indexOf("-rot")) + ".jpg";
  } else {
	current_img.src = current_img.src.substring(0, current_img.src.lastIndexOf(".")) + "-rot.jpg";
  }
}