var banner = new Array();

banner[0]='https://i.servimg.com/u/f69/14/49/20/39/unstol15.jpg';
banner[1]='https://i.servimg.com/u/f69/14/49/20/39/unstol16.jpg';
banner[2]='https://i.servimg.com/u/f69/14/49/20/39/unstol15.jpg';

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

setInterval("document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];",2000);