reCAPTCHA is a freely available CAPTCHA implementation. It distinguishes humans from computers. To use reCAPTCHA, you will need a public/private API key pair, available here: http://recaptcha.net/api/getkey.
reCAPTCHA Mailhide helps you protect your inbox by asking people to solve a reCAPTCHA before they can view your email address. The reCAPTCHA can only be solved by humans, so this stops spammers from gaining access to your email address through automated programs. reCAPTCHA Mailhide also requires a public and a private API key, that can be generated here: http://mailhide.recaptcha.net/apikey.
To install the package with pear just do:
$ pear install Services_ReCaptcha
And to uninstall it:
$ pear uninstall Services_ReCaptcha