var iValue, rNumber;

var img1 = new Image();
var img2 = new Image();
var img3 = new Image();
img1.src = "images/classimg1.jpg";
img2.src = "images/classimg2.jpg";
img3.src = "images/classimg3.jpg";


function displayImage(){
iValue = Math.random() * 3;
rNumber = Math.ceil(iValue);
if(rNumber==0) rNumber++;
document.image1.src=eval("img" + rNumber + ".src");
}