arImages=new Array(
 
  "images/seminar2.jpg",
  "images/seminar3.jpg",
  "images/seminar4.jpg",
  "images/seminar5.jpg"
);

rand=Math.floor(arImages.length*Math.random());
document.write('<img src="'+arImages[rand]+'" width="177" height="228" alt="Collaborative Learning">');