We understand that the world wide web is a big, scary thing for most people, so each month we’ll try to take a word, acronym or phrase and explain to you in simple, ‘non-techie’ terms what it all means. This is DBG’s Digital Definition of the Month!

So what is a CAPTCHA?  Well this is what the letters stand for:


Completely Automated Public Turing


test to tell


Computers and Humans Apart


You may have seen these tests at the bottom of contact forms on websites, or perhaps on the comments section of a blog.   The website user is forced to enter the letters and/or numbers from an image that is usually distorted or blurred in some way:


Image Source: www.captcha.net


The idea is that legitimate website users (i.e. humans) are easily able to decipher these, and therefore only quality entries are submitted.  Bots (or computers) are unable to read these and as such can’t submit automated posts.

The CAPTCHA.net website gives a great summary of the applications of CAPTCHAs online:

  • preventing comment spam in blogs
  • protecting website registration
  • protecting email addresses from scrapers
  • ensuring validity of online polls
  • preventing dictionary attacks in password systems
  • stopping search engine bots from indexing a web page

CAPTCHA codes are great for mimimising – or even stopping – spam form submissions, however they do pose issues for website users who have a disability related to their vision.  This should be kept in mind for websites who may have a user group that specifically encompasses people who may be visually-impaired.


Google reCAPTCHA

The Google reCAPTCHA project is an interesting one as they utilise the human effort required to solve a CAPTCHA for something positive:

“reCAPTCHA digitizes books by turning words that cannot be read by computers into CAPTCHAs for people to solve.  Word by word, a book is digitized and preserved online for people to find and read.”

So next time you get frustrated by another CAPTCHA code, think of how your energy is being channeled into the greater good!