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What is reCAPTCHA?

reCAPTCHA is an anti-spam method originating from Carnegie Mellon University which uses CAPTCHAs in a genius way. Instead of randomly generating useless characters which users grow tired of continuosly typing in, risking the possibility that spammers will eventually write sophisticated spam bots which use OCR libraries to read the characters, reCAPTCHA uses a different approach. They effectively kill two birds with one stone.

Digitizing of Books

If you didn’t know, the world is in the process of digitizing books (Even the Library of Congress is too) so that they can last forever as well as become searchable. To digitize the books, Scanners scan the pages of the books resulting in image files. OCR technology is then used to attempt to convert the images to text. Sometimes, however, certain words are illegible to the OCR technology but the good thing is that they know when the technology knows when this happens and can mark the words and put them into a repository. To construct a CAPTCHA, reCAPTCHA takes one of the words from these repositories and couples it with a word they do know, then distorts them some more. When a certain percentage of people type in the same spelling for the unknown word, it is assumed to be correct and sent back to help with the digitization process.

A typical reCAPTCHA form

How is this any better?

This effectively means that users who fill in reCAPTCHA forms can feel good knowing they are contributing to the digitizing of books all over the world, so it gives it a purpose. Also, if Industry Standard OCR Scanners can’t read certain words, add to that the fact that they are further distorted before being added to a CAPTCHA, one can be almost certain that Spam Bots won’t be able to read the CAPTCHAs either, this makes it secure.

reCAPTCHA has many security measures including IP Address Detection to review and potentially block IPs which have solved too many CAPTCHAs in a limited amount of time and adaptive security meaning they can fix bugs if they’re found, as they are found because the CAPTCHAs are generated on their servers (Meaning less load for you as well). But what if someone hosts a reCAPTCHA on their website, collects answers from their visitors and submits the answers to your site? Well that’s why reCAPTCHA uses a key system to authenticate. The keys are domain specific meaning you will need new ones for each domain you want to use reCAPTCHA on (Though this doesn’t apply to sub-domains). There is a public key and private key which are client-side and server-side respectively.

Many popular websites such as Twitter, Facebook, and even certain Government Websites like the TV Converter Box Coupon site are using reCAPTCHA. It is definitely becoming more and more widespread, and the neat thing is that it is accessible to everyone.

Is it working?

Take a look at this page which shows just how accurate and efficient reCAPTCHA is at transcribing literature to electronic form.

MailHide EMail Protection

Another project from reCAPTCHA is email protection. They call it MailHide. MailHide takes email addresses and encrypts them so that it becomes impossible for spam bots to take and add to their spam lists. MailHide generates a link which users click on to reveal the address. Once this link is clicked, they solve a simple reCAPTCHA form and the email is revealed. Email addresses that are hidden by MailHide show up by default like so: myem…@emailserver.com. Users then click on the three dots in the middle, solve the reCAPTCHA form that appears, and the email is revealed. This is just one way of putting reCAPTCHA forms to good use. Google is already using a similar method in their Google Groups site.

WordPress Plugin Features

Some of the many features that the WordPress reCAPTCHA Plugin includes are:

• Choice of reCAPTCHA anti-spam in:
  • Comments
  • Registration Form
• Language support:
  • English
  • Dutch
  • French
  • German
  • Portuguese
  • Russian
  • Spanish
  • Turkish
• Themes:
  • Red
  • White
  • Black Glass
  • Clean
• XHTML 1.0 Strict Compliance
• Tab Index customization on the comments post form
• HTTPS / SSL Support
• MailHide integration for email address protection. For example: bla...@gmail.com
  • mcrypt module detection
  • nohide BBCode tags to bypass email address protection
• Option to have admins exempt from reCAPTCHA forms and/or MailHide email protection
• Separate stylesheet for styling purposes (i.e. styling of protected emails)
• Can now work while Akismet is enabled (Though there shouldn’t be a reason to have it enabled while this is)

As if all this weren’t enough, WP-reCAPTCHA is also WordPress MU compatible!

Installation

The installation of the plugin is really simple: Simply download the archive, extract it and upload the wp-recaptcha folder to your wp-content/plugins folder. Finally, activate the plugin in the Administration interface.

For instructions on installing with WordPress MU (In two possible configurations), please refer to the Installation Section on the plugin’s page at the WordPress Plugins Repository.

Requirements

The only requirements for this plugin are that you get the API keys for reCAPTCHA here and if you plan on using MailHide email protection, get the API keys for that here.

If you plan on using MailHide, you will need to have the mcrypt PHP module loaded (Most servers do).

If you want XHTML 1.0 Compliance you and your users will need to have Javascript enabled. If you would like to have XHTML 1.0 Compliance while having support for non-Javascript users, read this.

FAQ

Why am I getting “Warning: pack() [function.pack]: Type H: illegal hex digit”?

You have the keys in the wrong place. Remember, the reCAPTCHA keys are different from the MailHide keys. And the Public keys are different from the Private keys as well. You can’t mix them around. Go through your keys and make sure you have them each in the correct box.

Help! I Still See Spam in my Spam Queue!

Please refer to the FAQ at WordPress.Org.

If you have any problems, you can comment here, make a post on the WordPress Forums with the tag wp-recaptcha, or use the Google Code Issue Tracker.

You can download the latest version of WP-reCAPTCHA from the WordPress Plugin Page.