var banner = new Array();

banner[0]='https://i.servimg.com/u/f31/13/31/89/73/banner122.jpg';
banner[1]='https://i.servimg.com/u/f31/13/31/89/73/banner122.jpg';
banner[2]='https://i.servimg.com/u/f31/13/31/89/73/banner122.jpg';
banner[3]='https://i.servimg.com/u/f31/13/31/89/73/banner122.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)];",3000);