if (document.getElementById) { window.onload = swap };

function swap() {
var numimages=6;
rndimg = new Array("../images/header_dadsonkayack.jpg", "../images/header_momkidsrunning.jpg", "../images/header_piggybackride.jpg", "../images/header_bikers.jpg", "../images/header_mountainfreedom.jpg", "../images/header_surfer.jpg"); 
x=(Math.floor(Math.random()*numimages));
randomimage=(rndimg[x]);
document.getElementById("header_image").style.backgroundImage = "url("+ randomimage +")"; 
}