var banner = new Array();

banner[0]='https://i.servimg.com/u/f20/12/70/30/37/banner14.jpg';
banner[1]='https://i.servimg.com/u/f80/12/70/30/37/logocl10.jpg';
banner[2]='https://i.servimg.com/u/f60/12/70/30/37/mgpw10.jpg';

document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];

setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",5000);