if (document.getElementById) { window.onload = swap };
 
function swap() {
var numimages=7;
rndimg = new Array("images/header-bg0.jpg", "images/header-bg.jpg", "images/header-bg1.jpg", "images/header-bg0.jpg", "images/header-bg.jpg", "images/header-bg1.jpg", "images/header-bg0.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("header-text").style.backgroundImage = "url("+ randomimage +")"; 
}