var banner = new Array();

banner[0]='https://i.servimg.com/u/f43/16/63/73/60/fotos_18.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);