function swapPic() {
	if(document.getElementById) {
		var thePicture=document.getElementById("bgImage");
		var picPath="images/bg/pic"+rnd(4)+".jpg";
		thePicture.style.background="url("+picPath+")";
	}
}
     
function rnd(n) {
	return Math.floor(Math.random() * n) + 1;
}