var banner = new Array();

banner.push('https://nsa25.casimages.com/img/2011/04/30/110430043304824515.png');
banner.push('https://nsa26.casimages.com/img/2011/04/30/110430043506202219.png');
banner.push('https://nsa25.casimages.com/img/2011/04/30/110430043546948884.png');
banner.push('https://nsa26.casimages.com/img/2011/04/30/110430043635367091.png');

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