var banner = new Array();

banner[0]='https://i.servimg.com/u/f22/16/42/65/34/i_logo10.jpg';
banner[1]='https://i.servimg.com/u/f22/16/42/65/34/pokemo11.jpg';
banner[2]='https://i.servimg.com/u/f22/16/42/65/34/pikach10.jpg';
banner[3]='https://i.servimg.com/u/f22/16/42/65/34/010.jpg';
banner[4]='https://i.servimg.com/u/f22/16/42/65/34/pokemo12.jpg';

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