var banner = new Array();

banner[0]='https://i.servimg.com/u/f67/15/07/40/40/9qv4na12.jpg';
banner[1]='https://i.servimg.com/u/f67/15/07/40/40/2eycj611.jpg';
banner[2]='http://i44.tinypic.com/24qqweq.jpg';

document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];
setInterval("document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];",4000);