function RandNum(max) {
  key = Math.floor(Math.random() * max);
  return key;
}

function RandomPicture() {
  images = new Array(4);

  images[0] = '<img src="http://www.ces.fas.harvard.edu/german_studies/imgs/berlin-wall4.jpg" class="front_img">';
  images[1] = '<img src="http://www.ces.fas.harvard.edu/german_studies/imgs/hannespic.jpg" class="front_img">';
  images[2] = '<img src="http://www.ces.fas.harvard.edu/german_studies/imgs/wzb.jpg" class="front_img">';
  images[3] = '<img src="http://www.ces.fas.harvard.edu/german_studies/imgs/reichstag.jpg" class="front_img">';

  
  key = RandNum(images.length);

//  document.write("Displaying image " + (key + 1) + " of " + images.length + ".<p>" );
  document.write(images[key]);
}