Integrated Joomla captcha (reCAPTCHA) does not appear in the front end.
Issue was caused by invalid reCAPTCHA API URL address.
To fix had to make changes to recaptcha.php file located in plugins/captcha/recaptcha
Change: const RECAPTCHA_API_SERVER = "http://api.recaptcha.net";
To: const RECAPTCHA_API_SERVER = "http://www.google.com/recaptcha/api";