var banner = new Array();

banner[0]='https://i.imgur.com/pYG9M.png';
banner[1]='https://i.imgur.com/rr06V.png';
banner[2]='https://i.imgur.com/LWh4i.png';
banner[3]='https://i.imgur.com/OGVNg.png';


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