var banner = new Array();

banner[0]='https://i.servimg.com/u/f60/14/90/34/68/logo0110.png';
banner[1]='https://i.servimg.com/u/f60/14/90/34/68/logo0210.png';
banner[2]='https://i.servimg.com/u/f60/14/90/34/68/logo0310.png';
banner[3]='https://i.servimg.com/u/f60/14/90/34/68/logo0410.png';
banner[4]='https://i.servimg.com/u/f60/14/90/34/68/logo0510.png';

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