document.write("<div id='headerimage' onclick='getrandomimage();'></div>");
function getrandomimage(){
	var random;
	var headerimage = document.getElementById("headerimage");
	//generate a random number between 0 and 8.
	random = Math.round(Math.random() * 8);
	headerimage.innerHTML = "<img src='images/headerimages/header" + (random) + ".gif'>"
}
getrandomimage();
window.setInterval("getrandomimage();", 20000);