Drupal 7 Captcha in all webforms or per content type webforms
You could add the following code to your template.php 

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


this should be placed inside the yourthemename_form_alter