error crítico en código captcha para evitar spam

[leskolpykos]

esto es lo que coloqué y no hace absolutamente nada ni detecta si es correcto el codigo o no, ni guarda el mensaje del usuario ni nada deoxxxx porqueee?

Código:

<?php require_once('../home/conexion.php'); ?>
<?php

extract($_POST); 

session_start(); 
if(isset($_POST[content])) { 
if( $_SESSION['security_code'] == $_POST['security_code'] && !empty($_SESSION['security_code'] ) ) { 
// Insert you code for processing the form here, e.g emailing the submission, entering it into a database.  
unset($_SESSION['security_code']); 

function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") 
{
  $theValue = (!get_magic_quotes_gpc()) ? addslashes($theValue) : $theValue;

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;    
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? "'" . doubleval($theValue) . "'" : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO libro (id, usuario, email, mensaje) VALUES (%s, %s, %s, %s)",
                       GetSQLValueString($_POST['id'], "int"),
                       GetSQLValueString($_POST['usuario'], "text"),
                       GetSQLValueString($_POST['email'], "text"),
                       GetSQLValueString($_POST['mensaje'], "text"));

  mysql_select_db($database_localhost);
  $Result1 = mysql_query($insertSQL) or die(mysql_error());

  $insertGoTo = "default.php";
  if (isset($_SERVER['QUERY_STRING'])) {
    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
    $insertGoTo .= $_SERVER['QUERY_STRING'];
  }
  header(sprintf("Location: %s", $insertGoTo));
} else { 
// Insert your code for showing an error message here 
echo "<script>alert('Disculpa! el código de seguridad está incorrecto'); window.location='javascript:history.back()';</script>"; 
} 
} 

?>