Implementere captcha i mailscript

Hej.

Jeg har et mailscript, som jeg gerne vil beskytte med en captchafunktion.

Jeg har fået sat selve captcha-billedet ind i min form:

<form method="post" action="sendt.php">
<fieldset>
<legend>Fill out all fields</legend>

<label for="t1">Name:</label>
<input id="t1" type="text" name="name" /><br />

<label for="t2">E-mail:</label>
<input id="t2" type="text" name="email" /><br />

<label for="t3">Subject:</label>
<input id="t3" type="text" name="subject" /><br />

<label for="t4">Message:</label>
<textarea id="t4" name="message" rows="10" cols="49"></textarea><br />

<label for="t5">Enter security code:</label>
<img src="captcha/CaptchaSecurityImages.php?width=100&height=40&characters=5" alt="captcha" />
<input id="security_code" name="security_code" type="text" />
<br />

<label for="t6">&nbsp;</label><input id="t6" type="submit" name="submit" value=" Send e-mail " /><br />
<input type="reset" value=" Clear " />
</fieldset>
</form>

- men jeg kan ikke finde ud af at indsætte sikkerhedskode-checket:

<?php
  session_start();
  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.
  } else {
      // Insert your code for showing an error message here
  }
?>

- i selve mailscriptet (sendt.php):

<?php

include_once("sql.php");
$ip = $_SERVER["REMOTE_ADDR"];

if (isset($_POST['submit']))
{
if (!empty($_POST['name']) && // there must be a name
!empty($_POST['email']) &&    // there must be an e-mail address
!empty($_POST['subject']) &&  // there must be a subject
!empty($_POST['message']) &&  // there must be a message

// more security checks
!strpos($_POST['name'], "@") &&
!eregi("\r",$_POST['name']) &&
!eregi("\n",$_POST['name']) &&
!eregi("\r",$_POST['email']) &&
!eregi("\n",$_POST['email']))

// everything ok, let's send e-mails...
{
  $headers = "From: ".$_POST['name']."<".$_POST['email'].">\n";
  $headers .= "Reply-To: ".$_POST['name']."<".$_POST['email'].">\n";
  $headers .= "X-Sender-IP: ".$ip."\n";
  $headers .= "MIME-Version: 1.0\n";
  $headers .="Content-Type: text/plain; charset=iso-8859-1 \n";

  $sql = "SELECT Email1 FROM ab_records";
  $result = mysql_query($sql);
  $i = 1;
  while($row = mysql_fetch_array($result)) {
      if (@mail($row[0], strip_tags($_POST['subject']),
      stripslashes(strip_tags($_POST['message'])), $headers))
      {
//      echo "True";
      }
      else
      {
      echo "E-mail no. ".$i." was not sent. An error ocurred.";
      }
      $i++;
  }
  echo "<p>E-mail sent. Thanks.</p>";
}
else
{
  echo "<p>The e-mail could not be sent. Fill out alle the fields and try again.</p>";
}
}

mysql_close();
?>

Jeg er løbet sur i if/else-sætningerne. Er der én, der kan hjælpe med at sætte sikkerhedskode-checket ind i mailscriptet?

På forhånd mange tak for hjælpen.