var banner = new Array();

banner[0]='https://i.servimg.com/u/f42/16/22/32/65/banner10.png';
banner[1]='https://i.servimg.com/u/f42/16/22/32/65/sonic_11.png';
banner[2]='https://i.servimg.com/u/f42/16/22/32/65/banner11.png';
banner[3]='https://i.servimg.com/u/f42/16/22/32/65/banner12.png';

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