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.

michael_greenberg

PHPEnkoder is a port of the excellent <a href="http://hivelogic.com/enkoder" rel="nofollow ugc">Hivelogic 
Enkoder</a> to PHP and, more specifically, 
to WordPress. It is used to display text in a way that users can see 
and bots can’t.
The encoding system is directly and unabashedly stolen from the 
BSD-licensed source of Hivelogic Enkoder, which works by randomly 
encoding a piece of text and sending to the browser self-evaluating 
Javascript that will generate the original text. This works in two 
ways: first, a bot must first have a fairly complete Javascript 
implementation (in particular, it must have <code>eval</code>); second, the 
decoding process can be made arbitrarily computationally 
intensive. This is similar to the idea of charging computational 
payments to send e-mail, only this is actually implemented.
By default, PHPEnkoder scrambles e-mails in plaintext and in <code>mailto:</code> 
links. It additionally provides a shortcode for manual scrambling, 
used like so: <code>[enkode text="shown to non-JS browsers"]this will be 
scrambled[/enkode]</code>.

PHPEnkoder

Encodes mailto: links and e-mail addresses with JavaScript to stifle webcrawlers.  Automatically turns plaintext e-mails into (enkoded) links.

Conditional CAPTCHA vs PHPEnkoder