captcha-module/application/component/oeusercomponent.php

<?php
/**
 * #PHPHEADER_OECAPTCHA_LICENSE_INFORMATION#
 */

/**
 * Article detailed information widget.
 */
class oeUserComponent extends oeUserComponent_parent
{
    /**
     * Class handling CAPTCHA image.
     *
     * @var object
     */
    protected $captcha = null;

    /**
     * Template variable getter. Returns object of handling CAPTCHA image
     *
     * @return object
     */
    public function getCaptcha()
    {
        if ($this->captcha === null) {
            $this->captcha = oxNew('oeCaptcha');
        }
        return $this->captcha;
    }

    public function createUser()
    {
        if(\OxidEsales\Eshop\Core\Registry::getConfig()->getRequestParameter('fnc') == 'approveOrder')
        {
            return parent::createUser();
        }

        if (!$this->getCaptcha()->passCaptcha()) {
            return false;
        }

        return parent::createUser();
    }
}