Beherit

Plugin protects WordPress website forms from spam and brute-force attacks with Google reCAPTCHA. There is no additional user-unfriendly options, just choose captcha version, enter keys and optionally set captcha theme, size or badge position – nothing more!
<h4>What forms are protected with reCAPTCHA?</h4>
<ul>
<li>Login form</li>
<li>Reset password form</li>
<li>New password form</li>
<li>Registration form</li>
<li>Comment form</li>
<li><a href="https://wordpress.org/plugins/lite-contact-form/" rel="ugc">Lite Contact Form</a></li>
<li>Contact Form 7</li>
</ul>
The reCAPTCHA verification will be required only for not logged in users.

GreCAPTCHA

Protects WordPress website forms from spam and brute-force attacks with Google reCAPTCHA.

Samir Shah

This plugin has two modes – basic and Akismet-enhanced.
Basic mode: the plugin will serve a CAPTCHA to all commenters that aren’t logged in and don’t have a previously approved comment. Repeat commenters will never see a CAPTCHA.
Akismet-enhanced mode (recommended): the plugin will serve a CAPTCHA only if Akismet identifies a comment as spam (much less frequently than the basic mode). Just install an activate <a href="https://wordpress.org/extend/plugins/akismet/" rel="ugc">Akismet</a> to enable this mode.
Note that a CAPTCHA will only appear after a comment is submitted. When a commenter is served a CAPTCHA:
<ul>
<li>If they fail, then the comment will be automatically discarded or trashed (and won’t clutter up your spam queue).</li>
<li>If they pass, it will be allowed into the spam queue (or approved, if you so choose). This means that any false positives from Akismet will be easily identified without you having to trawl through all the spam comments manually.</li>
</ul>
Most genuine commenters will be able to comment on your site hassle-free, without ever seeing a CAPTCHA.
The default CAPTCHA is a simple text-based test. There is also the option to use <a href="http://www.google.com/recaptcha" rel="nofollow ugc">reCAPTCHA</a> if you want something more robust (free API key required). You can also style the CAPTCHA page to fit with your own WordPress theme.
If you come across any bugs or have suggestions, please use the plugin support forum or <a href="http://rayofsolaris.net/contact/" rel="nofollow ugc">email me</a>. I can’t fix it if I don’t know it’s broken! Please check the <a href="https://wordpress.org/extend/plugins/wp-conditional-captcha/faq/" rel="ugc">FAQs</a> for common issues.
Thanks to the following people for contributing translations of this plugin: Belorussian – <a href="http://pc.de" rel="nofollow ugc">Marcis G</a>, Brazilian Portuguese – Stefano, Czech – <a href="http://trumplin.com/" rel="nofollow ugc">Ted</a>, Danish – Jesper, Dutch – <a href="http://wpwebshop.com/books/" rel="nofollow ugc">Rene</a>, Estonian – <a href="http://www.itransition.com" rel="nofollow ugc">Itransition</a>, Finnish – Jani, French – <a href="http://android-software.fr" rel="nofollow ugc">Laurent</a>, German – <a href="http://jochenpreusche.com" rel="nofollow ugc">Jochen</a>, Hindi – <a href="http://outshinesolutions.com" rel="nofollow ugc">Outshine Solutions</a>, Hungarian – <a href="http://www.televizio.sk" rel="nofollow ugc">Gyula</a>, Italian – <a href="http://gidibao.net" rel="nofollow ugc">Gianni</a>, Lithuanian – Mantas, Polish – <a href="http://www.spin.siedlce.pl" rel="nofollow ugc">Pawel</a>, Romanian – <a href="http://simplu.mixnet.ro" rel="nofollow ugc">Lotus</a>, Russian – <a href="http://www.everycloudtech.com/" rel="nofollow ugc">Ivanka</a>, Spanish – <a href="http://www.reinventia.net" rel="nofollow ugc">Reinventia</a>, Swedish – <a href="http://www.umu.se" rel="nofollow ugc">Hugo</a>, Turkish – Tony, Ukranian – <a href="http://www.everycloudtech.com/" rel="nofollow ugc">Ivanka</a>. Some of these translations are a bit out of date – updates welcome!

Conditional CAPTCHA

Asks commenters to complete a simple CAPTCHA if they don't have a previously approved comment, or if Akismet thinks their comment is spam.

GreCAPTCHA vs Conditional CAPTCHA