function showPic(whichpic, alt) {
 if (document.getElementById) {
  document.getElementById('mainimg').src = whichpic.href;
  if (alt != '') {
   document.getElementById('img_descr').childNodes[0].nodeValue = alt;
  } else {
   document.getElementById('img_descr').childNodes[0].nodeValue = ' ';
  }

  return false;
 } else {
  return true;
 }
}