Форум

$cpt = new CCaptcha();
$cpt->SetCode();

<input type="hidden" name="captcha_sid" value="<?= $cpt->GetSID() ?>">

<input type="text" size="10" name="captcha_word">

$cpt->CheckCode($_POST['captcha_word'], $_POST['captcha_sid'])

include_once($_SERVER["DOCUMENT_ROOT"]."/bitrix/modules/main/classes/general/captcha.php");