function get_element (identifier) {
  var element = null;
  if (document.getElementById) element = document.getElementById(identifier);
  else if (document.all) element = document.all.identifier;
  return(element);
}

function show_image (a) {
  var iv;
  var top;
  if (iv = get_element('imageviewer')) {
    if (window.pageYOffset) top = window.pageYOffset;
    else if (document.documentElement.scrollTop) top = document.documentElement.scrollTop;
    else if (document.body.scrollTop) top = document.body.scrollTop;
    else top = 0;
    if (top < 10) top = 10; 
    iv.style.top = String(top) + 'px';
    iv.innerHTML = '<img src="' + a + '" alt="Bild" title="Zum Schließen ins Bild klicken..." />';
    iv.style.display = 'block';
    return(false);
  }
  return(true);
}

function hide_image () {
  var iv;
  if (iv = get_element('imageviewer')) {
    iv.style.display = 'none';
    iv.innerHTML = '';
  }
  return(true);
}