var a = document.referrer; 
  var b = "";
  if (a.length) {
  	
    for (i = 0; i < a.length; i++) {
      if (a.substring(i,i+1) == "/") { b = b + "+"; } else { b = b + a.substring(i,i+1); }
    }
  document.writeln('<img src="/callback.php?ref_url='+ escape(a) + '" width="1" height="1"  />');
  }