var banner = new Array();

banner[0]='https://i.servimg.com/u/f37/17/57/44/98/310.jpg';
banner[1]='https://i.servimg.com/u/f37/17/57/44/98/210.jpg';
banner[2]='https://i.servimg.com/u/f37/17/57/44/98/410.jpg';
banner[3]='https://i.servimg.com/u/f37/17/57/44/98/610.jpg';

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