function selectPhoto() {
  // create an array of all possible images
  var photoArray = new Array('http://www.shssa.org/images/onload/photo_01.gif',
  'http://www.shssa.org/images/onload/photo_02.gif','http://www.shssa.org/images/onload/photo_03.gif',
  'http://www.shssa.org/images/onload/photo_04.gif','http://www.shssa.org/images/onload/photo_05.gif',
  'http://www.shssa.org/images/onload/photo_06.gif','http://www.shssa.org/images/onload/photo_07.gif',
  'http://www.shssa.org/images/onload/photo_08.gif','http://www.shssa.org/images/onload/photo_09.gif',
  'http://www.shssa.org/images/onload/photo_10.gif','http://www.shssa.org/images/onload/photo_11.gif',
  'http://www.shssa.org/images/onload/photo_12.gif','http://www.shssa.org/images/onload/photo_13.gif',
  'http://www.shssa.org/images/onload/photo_14.gif','http://www.shssa.org/images/onload/photo_15.gif',
  'http://www.shssa.org/images/onload/photo_16.gif','http://www.shssa.org/images/onload/photo_17.gif'); 
  // select a random num between 0 and length of the array
  var randomNum = Math.floor(Math.random() * photoArray.length);
  // assign a random array entry to the src of the image 
  document.getElementById("sahtuPhoto").src = photoArray[randomNum]; 
}