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NEW! With support for Elementor Form Widget.
Eazy C(omment)F(orm) Captcha adds a mathematic exercise to the comment form, contact form 7 & elementor, preventing bots to spam your comments and forms. Now with Elementor & Contact Form 7 support!
You can easily customize the label text for the captcha in the backend of WordPress. Also you can change the HTML Markup if you like.
With support for Contact Form 7.

Eazy CF Captcha

Eazy C(omment)F(orm) Captcha adds a mathematic exercise to the comment form, contact form 7 & elementor, preventing bots to spam your comments and …

Collins Agbonghama

A simple plugin for adding the new No CAPTCHA reCAPTCHA by Google to WordPress login, registration and comment system as well as BuddyPress registration form to protect against spam.
Features
<ul>
<li>Option to activate CAPTCHA in login, registration, comment and BuddyPress registration forms.</li>
<li>Choose a theme for the CAPTCHA.</li>
<li>Auto-detects the user’s language.</li>
</ul>
<h3>Plugins you will like</h3>
<ul>
<li><a href="https://wordpress.org/plugins/no-captcha-recaptcha-for-woocommerce/" rel="ugc">No CAPTCHA reCAPTCHA for WooCommerce</a>: Protect WooCommerce login, registration and password reset form against spam using Google’s No CAPTCHA reCAPTCHA.</li>
<li><a href="https://wordpress.org/plugins/ppress/" rel="ugc">ProfilePress</a>: A shortcode based WordPress form builder that makes building custom login, registration and password reset forms stupidly simple. <a href="http://profilepress.net" rel="nofollow ugc">More info here</a></li>
<li><a href="https://wordpress.org/plugins/mailoptin/" rel="ugc">MailOptin</a> – The best WordPress email optin forms, email automation & newsletters plugin in the market.</li>
</ul>

No CAPTCHA reCAPTCHA

EDIT: The problems described below have been improved by Collins Agbonghama. I haven't verified, but I'm going to upgrade from 4-stars to a 5-star review for taking care of the issues I faced a few months ago :)

A couple issues with this plugin, all of which can easily be fixed (and let me know if they do get fixed, I will happily add that star back into it!)

First, I'm using a custom theme with very few modifications, and no modifications to the backend. So these would likely affect a vanilla WordPress install.

Issue #1) The settings page for this plugin is a massive menu item. It's the only link in the menu that takes up two lines. And it's a page you only need to use once. The link should be moved to the Settings menu, as a submenu item.

Screenshot of #1: https://s3-us-west-2.amazonaws.com/elasticbeanstalk-us-west-2-868470985522/ShareX/2017/04/chrome_2017-04-29_14-14-25.png

Issue #2) The ReCaptcha widget is clearly lacking some bottom margin on the login screen. It's almost touching the button to sign in. This issue can easily fixed with CSS, but for some reason it was neglected.

Screenshot of #2: https://s3-us-west-2.amazonaws.com/elasticbeanstalk-us-west-2-868470985522/ShareX/2017/04/chrome_2017-04-29_14-15-26.png

Issue #3) The default verbiage for the recaptcha error can only be described as poor English. Thankfully you can change it, but you are going to want to change it on every site. The default is currently "ERROR: Please retry CAPTCHA". It is important to note that the "No Captcha" ReCAPTCHA is not a captcha. That's the whole point. Captchas involve letters. The error should say something like:

"ERROR: Please retry ReCAPTCHA" - at the very least, refer to the brand as this is NOT a regular captcha field.

"ERROR: Please confirm you are not a robot"

"ERROR: Please check the box below to prove you are a human"

etc.

Everything else looks good. These are quite nit-picky "issues" too. So unless these really bother you, this is a worthwhile plugin.

Hopefully these issues can be fixed and this becomes a stellar plugin! Thanks!

Works, but needs improvement (Improved 9/18/2017)

thanks

Protect WordPress login, registration, comment and BuddyPress registration forms with Google's No CAPTCHA reCAPTCHA.

Eazy CF Captcha vs No CAPTCHA reCAPTCHA