arimages=new Array(
  "images/img1.jpg",
  "images/img2.jpg",
  "images/img3.jpg",
  "images/img4.jpg",
  "images/img5.jpg",
  "images/img6.jpg",
  "images/img7.jpg",
  "images/img8.jpg",
  "images/img9.jpg"
);

rand=Math.floor(arimages.length*Math.random());
document.write('<img src="'+arimages[rand]+'" width="368" height="230" alt="Rotating images of The Instructional Services Center">');