var banner = new Array();

banner[0]='https://i1246.photobucket.com/albums/gg610/freakdik/logo.png';
banner[1]='https://i1083.photobucket.com/albums/j398/Zombitch31/sample1-1.png';

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