var banner = new Array();

banner[0]='https://i196.photobucket.com/albums/aa313/Rata_13/mario.jpg';
banner[1]='https://i196.photobucket.com/albums/aa313/Rata_13/metroid.jpg';
banner[2]='https://i196.photobucket.com/albums/aa313/Rata_13/zelda.jpg';
banner[3]='https://i196.photobucket.com/albums/aa313/Rata_13/pokebola.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);