captcha do formulara

<?php
$mess = "Sprava z webu: \n";
$mess .= "Meno:" . $_POST['nick'] . "\n";
$mess .= "Mail:" . $_POST['email'] . "\n";
$mess .= "ICQ:" . $_POST['icq'] . "\n";
$mess .= "Typ webu:" . $_POST['typ'] . "\n";
$mess .= "Doplnky:" . $_POST['doplnky'] . "\n";


mail("kajbo@atlas.sk","Predmet","$mess");
?>

<p align="center"><span class="txt_nadpis">e-mail bol odoslaní</span></p>

<span class="txt_nadpis">
Objednávka
</span><br><br>
<span class="txt_text" style="position: absolute; ">
 <form method="POST" action="index.php?id=pos">
Meno: &nbsp;&nbsp; <input type="text" name="nick" id="nick" size="30"><br><br>
Email:&nbsp;&nbsp; &nbsp;<input type="text" name="email" id="email" size="30" value="@"><br><br>
ICQ:&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;<input type="text" name="icq" id="email" size="30"><br><br><br>
Typ webu: <input type="text" name="typ" id="email" size="50"><br><br>
Doplnky: &nbsp;&nbsp; <input type="text" name="doplnky" id="email" size="50"><br><br>
<input type="submit" value="Odoslat" style='border: 2px solid #2e5f89; background-color: #4b7fac; color: #ffffff; font-weight: bold;'>
</form><br>
Ak by nastali nejaké problémy, kontaktujte ma na kajbo@atlas.sk
</span>