var banner = new Array();

banner[0]='http://data0.eklablog.fr/bit-lit/perso/gifs%20forum/banniere%20empreintes%20continu.gif';
banner[1]='http://data0.eklablog.fr/bit-lit/perso/gifs%20forum/banniere%20jenks%20continu.gif';

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