var banner = new Array();

banner[0]='https://i1207.photobucket.com/albums/bb477/m4321/pikachulogocpia-3.png';
banner[1]='https://i1207.photobucket.com/albums/bb477/m4321/tsutarjalogocpia.png';
banner[2]='https://i.servimg.com/u/f47/14/97/30/98/mijuma10.png';

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