Contact form with captcha plugin allows you to use a Google reCAPTCHA contact form on your blog. It requires PHP 5.0 or later.
You can use it in any post or page by inserting the shortcode
You can get them from the Google reCAPTCHA website(http://www.google.com/recaptcha/whyrecaptcha "Google reCAPTCHA website").
reCAPTCHA Form can be installed alongside any other plugins that use the reCAPTCHA challenge system, however you must make sure that whatever post/page you insert the reCAPTCHA Form shortcode on does not already display a reCAPTCHA form - this is because you cannot display more than one reCAPTCHA form on the same web page.