var banner = new Array();

banner.push('https://i.servimg.com/u/f20/13/60/54/50/banni-15.jpg');
banner.push('https://i.servimg.com/u/f20/13/60/54/50/sans_t11.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)];",3000);