if (document.getElementById) { window.onload = swap };
function swap() {
var numimages=15;
rndimg = new Array("images/0.jpg", "images/1.jpg", "images/2.jpg", "images/3.jpg", "images/4.jpg", "images/5.jpg", "images/6.jpg", "images/7.jpg", "images/8.jpg", "images/9.jpg", "images/10.jpg", "images/11.jpg", "images/12.jpg", "images/13.jpg", "images/14.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("Content").style.backgroundImage = "url("+ randomimage +")"; 
}