img = new Array();
 img[0] = "images/img_c0.jpg";
 img[1] = "images/img_c1.jpg";
 img[2] = "images/img_c2.jpg";
 img[3] = "images/img_c3.jpg";
 img[4] = "images/img_c4.jpg";
 n = Math.floor(Math.random()*img.length);
 document.write("<img src='"+img[n]+"' border='0'>");