var numimages = 5;
function insertRandomPic(path) {
  var number = Math.round(Math.random()*numimages + 0.5);
  window.document.write("<a href=\"" + path + "/gruppe_big" + number + ".jpg\" target=\"bigPic\">");
  window.document.write("<img class=\"group" + number + "\" src=\"" + path + "/sgb_gruppe" + number + ".jpg\" alt=\Gruppenfoto der MK St. Georg\"></a>");
}