var img_name = new Array("pics/128.jpg", "pics/131.jpg", "pics/137.jpg", "pics/139.jpg", "pics/142.jpg", "pics/145.jpg", "pics/pics052.jpg", "pics/pics045.jpg","pics/pics047.jpg", "pics/pics048.jpg", "pics/pics049.jpg", "pics/pics050.jpg", "pics/pics051.jpg", "pics/students001.jpg");

var l = img_name.length;

var rnd_no = Math.round((l-1)*Math.random());

document.r_img.src = img_name[rnd_no];