var banner = new Array();

banner.push('https://nsa29.casimages.com/img/2012/08/28//120828032105108540.png');
banner.push('https://nsa30.casimages.com/img/2012/08/28//120828032045134151.png');
banner.push('https://nsa30.casimages.com/img/2012/09/06//120906021741227423.png');
banner.push('https://nsa30.casimages.com/img/2012/09/06//120906025629625482.png');

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