Jehy

<a href="https://wordpress.org/plugins/securimage-wp-fixed/" rel="ugc">Securimage-WP-Fixed</a> utilizes the powerful CAPTCHA protection of <a href="http://phpcaptcha.org/" title="Securimage PHP CAPTCHA" rel="nofollow ugc">Securimage Captcha</a> which adds protection to your WordPress comment forms. Unfortunately, it didn’t have option to be installed on user register page. Now you can just install Securimage-WP-REG, enable it – and you will have CAPTCHA on register page!
So, Securimage-WP-REG adds captcha on register pages.
Requirements:
<ul>
<li><a href="https://wordpress.org/plugins/securimage-wp-fixed/" rel="ugc">Securimage-WP-Fixed</a> plugin installed and working. Old version of this plugin you can find <a href="https://www.phpcaptcha.org/download/wordpress-plugin/" rel="nofollow ugc">here</a>.</li>
</ul>
<h4>Donate or help?</h4>
If you want to ensure the future development and support of this plugin, you can make donation <a href="http://jehy.ru/articles/donate/" rel="nofollow ugc">on this page</a> or just write about this plugin in your blog.

Securimage-WP-REG

Securimage-WP-REG adds captcha ptotection from Securimage-WP plugin on register pages.

barpachuk

eranfl

clickcease

Bots and invalid traffic can reach your site through paid, organic, and direct traffic, resulting in a wasted ad budget and disrupted marketing funnels.
Prevent bots, competitors, and malicious users from damaging your marketing performance with ClickCease, the industry-leading service that keeps your website and ads safe from fraud. Quick installation and real-time protection for all your website’s incoming traffic.
ClickCease protects you from invalid traffic by monitoring and protecting your:
<ul>
<li>Paid traffic (Google, Facebook, & Microsoft)</li>
<li>Organic traffic</li>
<li>Direct traffic</li>
</ul>
Put a stop to ad and click fraud on your website with our market-leading AI software. Allow yourself to fully focus on growing your business without having online fraud distract you.
You will need an active ClickCease subscription to use this WordPress plugin.

ClickCease Click Fraud Protection

I'm not commenting on the ClickCease service - as far as I know, that's totally great, but this plugin is coded in the worst way imaginable. 

So much php processing and hogging of the output buffer unecessarily. 

Do not use this plugin. Just add the code to your theme's header manually. 

Worst Code Imaginable


Their support closes support requests without solving them


Strange service, no support, bad code

Protect your website and ad campaigns from bots, competitors, and click fraud with ClickCease's advanced fraud prevention and real-time monitoring.

Securimage-WP-REG vs ClickCease Click Fraud Protection