function showPreview(imagePath) {
  var subImages = document.getElementById('imgdisplay').getElementsByTagName('IMG');
  if(subImages.length == 0) {
    var img = document.createElement('IMG');
    document.getElementById('imgdisplay').appendChild(img);
  }
  else {
    img = subImages[0];
  }
  img.src = imagePath;
}