// background changer 

function setPic() {  
   var picHold = document.getElementById("header");  
   var pics = new Array("header-image1.jpg", "header-image2.jpg", "header-image3.jpg", "header-image4.jpg");
   var choose = Math.floor(Math.random()* pics.length);  
   picHold.style.background="url("+'../../images/'+pics[choose]+")";
}  
 
function addLoadEvent(func) {
	var oldonload = window.onload;
	if (typeof window.onload != 'function') {
		window.onload = func;
	} else {
		window.onload = function() {
			oldonload();
			func();
		}
	}
}

addLoadEvent(setPic);