var images = new Array();

images[1] = "images/random_center/01.jpg";
images[2] = "images/random_center/02.jpg";
images[3] = "images/random_center/03.jpg";
images[4] = "images/random_center/04.jpg";
images[5] = "images/random_center/05.jpg";
images[6] = "images/random_center/06.jpg";
images[7] = "images/random_center/07.jpg";

document.write('<img src='+images[Math.round((7*Math.random()+0.5))]+' width="200" height = "118" />');