var banner = new Array();

banner[0]='https://i.servimg.com/u/f42/17/52/41/41/23410.jpg';
banner[1]='https://i86.photobucket.com/albums/k92/potter_019/23sd410.png';

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