var banner = new Array();

banner[0]='https://i.servimg.com/u/f28/16/38/98/05/56624_12.jpg';
banner[1]='https://i.servimg.com/u/f28/16/38/98/05/39468811.jpg';
banner[2]='https://i.servimg.com/u/f28/16/38/98/05/42904210.jpg';
banner[3]='https://i.servimg.com/u/f28/16/38/98/05/49928810.jpg';

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