Pieter

By default WordPress will tell anyone trying to gain access what they did wrong when trying to bruteforce your site. This plugin hides the reason the login failed. This way an attacker will have a harder time getting in.

PD Login Security

Disables the default login errors, adding more security to the login form of your WordPress install.

Tareq Hasan

weDevs

Nizam Uddin

podpirate

Integrate reCaptcha in your blog. Supports no Captcha as well as old style recaptcha. 
Provides of the box integration for signup, login, comment formsand Ninja Forms as well 
as a plugin API for your own integrations.
<h4>Features:</h4>
<ul>
<li>Secures login, signup und comments with a recaptcha.</li>
<li>Supports old as well as new reCaptcha.</li>
<li>
Works together with
<ul>
<li>WP Multisite</li>
<li>bbPress</li>
<li>BuddyPress</li>
<li>AwesomeSupport (thanks to <a href="http://julienliabeuf.com/" rel="nofollow ugc">Julien Liabeuf</a> )</li>
<li>WooCommerce (Only checkout, registration and login form. Not password reset)</li>
<li><a href="http://ninjaforms.com/" rel="nofollow ugc">Ninja Forms</a></li>
<li>cformsII</li>
</ul>
</li>
<li>
For integration in your self-coded forms see this <a href="https://github.com/tareq1988/wp-recaptcha-integration/wiki/Custom-Themes-and-Forms" rel="nofollow ugc">wiki article</a> for details.
</li>
</ul>
<h4>Localizations</h4>
<ul>
<li>Brazilian Portuguese (thanks to <a href="http://www.viniciusferraz.com" rel="nofollow ugc">Vinícius Ferraz</a>)</li>
<li>Spanish (thanks to <a href="https://github.com/yivi" rel="nofollow ugc">Ivan Yivoff</a>)</li>
<li>Italian (thanks to <a href="http://blog.salaros.com/" rel="nofollow ugc">Salaros</a>)</li>
<li>German</li>
</ul>
Latest Files on GitHub: <a href="https://github.com/tareq1988/wp-recaptcha-integration" rel="nofollow ugc">https://github.com/tareq1988/wp-recaptcha-integration</a>
<h4>Compatibility</h4>
On a WP Multisite you can either activate the plugin network wide or on a single site.
Activated on a single site everything works as usual.
With network activation entering the API key and setting up where a captcha is required 
is up to the network admin. A blog admin can override the API key e.g. when his blog is 
running under his/her own domain name.
<h4>Known Limitations</h4>
<ul>
<li>
You can’t have more than one old style reCaptcha on a page. This is a limitiation of 
reCaptcha itself. If that’s an issue for you, you should use the no Captcha Form.
</li>
<li>
A No Captcha definitely requires client side JavaScript enabled. That’s how it does its 
sophisticated bot detection magic. There is no fallback. If your visitor does not have 
JS enabled the captcha test will not let him through.
</li>
<li>
On a Contact Form 7 when the reCaptcha is disabled (e.g. for logged in users) the field 
label will be still visible. This is due to CF7 Shortcode architecture, and can’t be fixed.
To handle this there is a filter <code>recaptcha_disabled_html</code>. You can return a message for your logged-in 
users here. Check out the <a href="https://github.com/tareq1988/wp-recaptcha-integration" rel="nofollow ugc">GitHub Repo</a> for details.
</li>
<li>
As of version 4.3 CF7 comes with its own recaptcha. Both are supposed to work together. 
I you want to keep the WP ReCaptcha functionality, e.g. if you want to hide the captcha 
from known users, leave the integration in the CF7 settings unconfigured.
</li>
<li>
Old style reCaptcha does not work together with WooCommerce.
</li>
<li>
In WooCommerce the reset password form can not be protected by a captcha. Woocommerce does 
not fire any action in the lost password form, so there is no way for the plugin to hook in. 
Take a look at <a href="https://wordpress.org/support/topic/captcha-not-showing-on-lost-password-page?replies=7" rel="ugc">this thread</a> for a workaround.
</li>
<li>
Due to a lack of filters there is no (and as far as one can see, there will never be) 
support for the MailPoet subscription form.
</li>
</ul>
<h3>Plugin API</h3>
The plugin offers some filters to allow themes and other plugins to hook in.
See <a href="https://github.com/tareq1988/wp-recaptcha-integration" rel="nofollow ugc">GitHub-Repo</a> for details.

ReCaptcha Integration for WordPress

This plugin is very robust. It replaces another reCAPTCHA plugin I was using. I like this one because it works with WooCommerce, and protects login, lost password, and commenting forms.

Very Robust. Easy To Setup

This was the only plugin I could find that added a Captcha to the WooCommerce guest checkout. All the others either need to be paid for or only add a captcha to the login and registration pages. I wish this plugin was more visible so I hadn't wasted time with inferior offerings.

Nice job weDevs and thanks!

Only plugin to add WooCommerce checkout Captcha

reCaptcha for login, signup, comment forms, Ninja Forms and woocommerce.

PD Login Security vs ReCaptcha Integration for WordPress