function popup(URL) {
	var windowleft = (screen.width-640)/2;
  	var windowtop = (screen.height-480)/2;
	eval("page" + " = window.open(URL, '" + "', 'toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=1,width=640,height=480,left='+windowleft+',top='+windowtop+'');");
	}

function changeBackground() {
	bg = document.getElementById('picture');
	bg.style.backgroundImage = 'url(/core/i/picture/'+(Math.floor(Math.random() * 6) + 1)+'.jpg)';
}