var r;
r=Math.ceil(Math.random()*4);
function rotate() {
	var randomadd=0; // Vary the interval by this number
	r++;
	if (r>4)
		r=1;
	document.getElementById('rotate').style.backgroundImage="url(images/topbild"+r+".jpg)";
	setTimeout('rotate()',(20+Math.ceil(Math.random()*randomadd))*1000);
}