Aside from being annoying, does CAPTCHA really serve a useful purpose? What is CAPTCHA? In short, CAPTCHA is an acronym standing for “Completely Automated Public Turing test to tell Computers and Humans Apart”. It describes pretty much any automated system that attempts to determine whether or not a user is human based on a simple test.

Recently, community member Roguekiller23231 asked, “What is CAPTCHA really used for?”

When you fill out a CAPTCHA form, you’re essentially telling the website that you’re a human being capable of reading (or in some cases hearing) the distorted word, phrase, or random characters. This is one method site administrators use to keep spammers from flooding the site with unwanted content.

There are likely hundreds of CAPTCHA services and scripts out in the world today. Some are automated and rendered by the site’s server once a request is made while others can be hosted and managed by an independent service off-site.

Some CAPTCHA systems, including reCAPTCHA, actually perform a dual purpose. By solving the CAPTCHA puzzle, the human on the other end may be contributing to the digitizing of books for online distribution. With reCAPTCHA, a series of characters may be selected by their servers that automated systems have a hard time identifying. Once solved, the solution is submitted and added to the digitized copy of the book.

Unfortunately, spammers have found ways around CAPTCHA. One popular method is hiring a team of people in another country to solve the CAPTCHA barriers for the spamming system. They are presented with a new CAPTCHA every time their system comes across one. Once solved, they move on to the next while the spam gets sent to the site automatically. Other ways of bypassing the barrier include finding flaws in implementation that can allow a system to go around the CAPTCHA entirely and through more advanced character recognition software.

With this in mind, there are many useful alternatives to CAPTCHA out there. If your site is built on WordPress, you may find a solution in plug-ins such as Akismet, Challenge, and others. These alternatives either provide a barrier that delays and/or deters a spammer from making their comment, or allows them through and flags potential spam for moderation. Unfortunately, no system currently available is absolutely foolproof short of moderating every comment with a human being prior to it being allowed on the site.