要使用joomla默认的recaptcha插件，请遵循以下步骤-

In order to use joomla default recaptcha plugin follow these steps-

1)从 http://www.google.com/recaptcha

2)将这些键设置为recaptcha插件，如果没有，则将其激活.

2)Set these keys to recaptcha plugin and activate it if it's not.

3)将下面的代码放在要显示Recaptcha的位置

3)Put below code where you want to show recaptcha

//php code
JPluginHelper::importPlugin('captcha');
$dispatcher = JDispatcher::getInstance();
$dispatcher->trigger('onInit','dynamic_recaptcha_1');

//html code inside form tag
<div id="dynamic_recaptcha_1"></div>

4)将此代码放在验证/处理表单的位置

4)Put this code where you validating/processing the form

$post = JRequest::get('post');      
JPluginHelper::importPlugin('captcha');
$dispatcher = JDispatcher::getInstance();
$res = $dispatcher->trigger('onCheckAnswer',$post['recaptcha_response_field']);
if(!$res[0]){
    die('Invalid Captcha');
}

//对于Joomla 3.x

//For Joomla 3.x

$post = JFactory::getApplication()->input->post;
$dispatcher = JEventDispatcher::getInstance();