dannyx

This is my first WordPress plugin that i made it for personal use and to learn how to build plugins. 
This plugin replaces the submit button on the post comment section with a set of buttons from images. 
A small message provides the user a hint on what button to use to submit the comment. 
Demo: http://www.arcweb.ro/blog/2011/12/21/testing-cutecaptcha-plugin/
Requirements: 
PHP mcrypt should be available on the server, i will add more encryption methods if required. 
Session support is optional, supports caching of post pages without session but with lower security.
Customize: 
All the information and parameters to configure are in cutecaptcha.php 
The images and messages can be customized and should be quite fun to adapt it with the 
subject of each website, especially expecting that anybody that wants to post a comment 
should have a good idea about that subject.
Security: 
The variety in images and messages will make it difficult for automated bots to break it. 
The plugin is intended for a regular blog that will never attract dedicated spamers. 
At this moment the association between messages and photos can be analyzed, but it is possible to add 
another layer of protection if required. I strongly suggest that each site uses personalized images and 
messages related to their content.
TODO: 
Alternative encryption functions for servers without php mcrypt. 
Extra layer of security on images: Raw data inserted in file, modified with 
variable watermarks for each session. 
Display a specific number of buttons from a gallery of buttons. 
IP Block: block ip’s after a number of failed submits for a number of days.

Cute Captcha

Replaces the submit button  with a set of buttons from a set of images. A small message provides the user a hint on what button to use.

webvitalii

kudlav

This is fork of successful Anti-spam plugin v5.5 written by webvitalii, for more info visit <a href="https://github.com/kudlav/anti-spam/" rel="nofollow ugc">GitHub Fork</a>. 
From version 5.6 maintained by kudlav.
<ul>
<li><a href="https://github.com/kudlav/anti-spam/" rel="nofollow ugc">GitHub</a></li>
</ul>
Anti-spam Reloaded plugin blocks 100% of automatic spam messages in comments section and also blocks all trackbacks.No captcha required.
Plugin is simple and easy to use: just install it and it just works.
Blocked comments can be stored in the Spam area and converted to regular comments if needed.
Anti-spam Reloaded plugin is GDPR compliant and does not store any other user data except of the behaviour mentioned above.
Plugin blocks spam only in comments section.. 
Plugin does not block manual spam (submitted by spammers manually via browser).
<h3>Compatibility</h3>
All modern browsers and IE11+ are supported. 
Anti-spam Reloaded plugin works with disabled JavaScript. Users with disabled JavaScript should manually fill current year before submitting the comment.
Server compatibility:
<ul>
<li>WordPress 3.3 – 6.5</li>
<li>PHP 5.6 – 8.2</li>
<li>Doesn’t use jQuery</li>
</ul>
Plugin is incompatible with:
<ul>
<li>Disqus</li>
<li>Jetpack Comments</li>
<li>AJAX Comment Form</li>
<li>bbPress</li>
</ul>
If site has caching plugin enabled and cache is not cleared or if theme does not use ‘comment_form’ action 
and there is no plugin inputs in comments form – plugin tries to add hidden fields automatically using JavaScript.
<h3>How does it work?</h3>
The blocking algorithm is based on 2 methods: ‘invisible js-captcha’ and ‘invisible input trap’ (aka honeypot technique).
<h4>‘invisible js-captcha’</h4>
The ‘invisible js-captcha’ method is based on fact that bots does not have JavaScript on their user-agents. 
Extra hidden field is added to comments form. 
It is the question about the current year. 
If the user visits site, than this field is answered automatically with JavaScript, is hidden by JavaScript and CSS and invisible for the user. 
If the spammer will fill year-field incorrectly – the comment will be blocked because it is spam.
<h4>‘invisible input trap’</h4>
The ‘invisible input trap’ method is based on fact that almost all the bots will fill inputs with name ’email’ or ‘url’. 
Extra hidden field is added to comments form. 
This field is hidden for the user and user will not fill it. 
But this field is visible for the spammer. 
If the spammer will fill this trap-field with anything – the comment will be blocked because it is spam.

Cute Captcha vs Anti-spam Reloaded