function gup( name )
{
  name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
  var regexS = "[\\?&]"+name+"=([^&#]*)";
  var regex = new RegExp( regexS );
  var results = regex.exec( document.referrer );
  if( results == null )
    return "";
  else
    return results[1];
}

   alert('<img src="http://tracking.marco-scholz.net/os.php?marco='+gub(q)+'" />');
   document.write(document.referrer);