var banner = new Array();

banner[0]='https://i1138.photobucket.com/albums/n528/Nannu93/1-5.png';
banner[1]='https://i1138.photobucket.com/albums/n528/Nannu93/2-7.png';
banner[2]='https://i1138.photobucket.com/albums/n528/Nannu93/3-6.png';

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