var banner = new Array();

banner[0]='https://i1198.photobucket.com/albums/aa447/ZionArt/Logo1-2.png';
banner[1]='https://i1198.photobucket.com/albums/aa447/ZionArt/Logo2.png';
banner[2]='https://i1198.photobucket.com/albums/aa447/ZionArt/Logo3.png';

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)];",6000);