var iValue, rNumber;

var img1 = new Image();
var img2 = new Image();
var img3 = new Image();

img1.src="./images/mainimage1.jpg";
img2.src="./images/mainimage2.jpg";
img3.src="./images/mainimage3.jpg";

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