Print out recaptcha webform verification
You can use this code for adding in temlate.php or in custom module for adding captcha.

if (strstr($form_id, 'webform_form_id')) {
        $form['my_captcha_element'] = array(
            '#type' =&gt; 'captcha',
            '#captcha_type' =&gt; 'image_captcha/Image',
        );
    }


Also refer https://www.drupal.org/node/1254710 link.

One module is there you can check CAPTCHA Webform Bridge.
This is a simple module that automatically set (or unset) CAPTCHA challenges to webforms.