var banner = new Array();

banner.push('https://i.servimg.com/u/f30/14/90/78/18/fond0210.jpg');
banner.push('https://i.servimg.com/u/f30/14/90/78/18/fond0110.jpg');

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