var banner = new Array();

banner.push('https://i.servimg.com/u/f77/14/27/27/99/baniie10.jpg');
banner.push('https://i.servimg.com/u/f77/14/27/27/99/bannie11.jpg');
banner.push('https://i.servimg.com/u/f77/14/27/27/99/baniie11.jpg');

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