window.onload = function ()
{
	var el = document.getElementById("header");

	var randNum = 0;
	var maxValue = 2;

	while (randNum > maxValue || randNum < 1) 
	{
		randNum = (Math.round((Math.random() * 10)))
	} 

	el.style.backgroundImage = 'url(/images/header' + randNum + '.jpg)';
}