var imglist = new Array(
      "image/img_main0.jpg",
      "image/img_main1.jpg",
     "image/img_main2.jpg",
      "image/img_main3.jpg",
//      "image/img_main4.jpg",
      "image/img_main5.jpg");
   var selectnum = Math.floor((Math.random() * 100)) % imglist.length;
   var output = "<img src=" + imglist[selectnum] + ">";
   document.write(output);