function selectdPopImage() {
  // create an array of all possible images
  var dPopArray = new Array('http://www.hlthss.gov.nt.ca/sites/drop_the_pop/images/header/better_smile_header.jpg',
  'http://www.hlthss.gov.nt.ca/sites/drop_the_pop/images/header/healthy_environment_header.jpg',
  'http://www.hlthss.gov.nt.ca/sites/drop_the_pop/images/header/better_concentration_header.jpg',
  'http://www.hlthss.gov.nt.ca/sites/drop_the_pop/images/header/strong_bones_header.jpg',
  'http://www.hlthss.gov.nt.ca/sites/drop_the_pop/images/header/keep_traditions_header.jpg',
  'http://www.hlthss.gov.nt.ca/sites/drop_the_pop/images/header/good_health_header.jpg'); 
  // select a random num between 0 and length of the array
  var randomNum = Math.floor(Math.random() * dPopArray.length);
  // assign a random array entry to the src of the image 
  document.getElementById("dropthePop").src = dPopArray[randomNum]; 
}