var banner = new Array();

banner.push('https://i.servimg.com/u/f57/16/09/60/26/hobbit11.jpg');
banner.push('https://i.servimg.com/u/f57/16/09/60/26/ouat1a10.jpg');
banner.push('https://i.servimg.com/u/f57/16/09/60/26/titre_10.jpg');

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