var req,image;

function getreq(){
	if(window.XMLHttpRequest) return new XMLHttpRequest();
	else if(window.ActiveXObject) return new ActiveXObject("Microsoft.XMLHTTP");
}


function changeBackground(thisimage){
	image= "images/backgrounds/"+thisimage;
	req = getreq();
	req.onreadystatechange = imagexists;
	req.open("get", image, true);
	req.send(null);		
}


function imagexists(){
	if(req.readyState == 4){
		if(req.status != 200) image = "images/backgrounds/default.jpg";
		document.getElementById('container').style.backgroundImage="url("+image+")";
	}
}