While browsing the web, you've probably encountered these weird combinations of letters and numbers that many websites use to check that you're human, and not a web robot or spammers. The idea behind it is that a human, in theory, can decipher those fuzzy characters and enter them in a form to prove he or she is not a computer, which would not be able to recognize those distorted letters. This method has been devised by researchers at Carnegie Mellon University and they called it CAPTCHA (Completely Automated Public Turing test to Tell Computers and Humans Apart). A Turing test, named after the computer scientist Alan Turing, is a type of test with the purpose to differentiate a human from a computer.


As a sighted person, have you ever wondered how a blind person is able to recognise the letters and numbers in the CAPTCHA? Given the fact CAPTCHAs are made so that computers cannot understand what they contain, not even screen readers will be able to do the job. CAPTCHAs, in their basic form, are not accessible. For this reason, accessibility features have been integrated in order to make CAPTCHAs accessible for those who have visual impairments. An example of an accessibility feature that some websites have integrated is a voice message reading out the individual characters with a confused and noisy voice. The audio is purposefully made very difficult to understand and still doesn't make it completely accessible.

How accessible is this voice message feature? Well, a user is able to correctly understand the audio message less than half of the time (46%). This whole procedure, on average, takes 65 seconds to be completed. In addition to this, blind users will have to use a braille note taker to jot down the numbers and digits they understand in order to try and enter them at the end of the audio playback. This is far, in my opinion, from being acceptable.

The W3 consortium is in charge of standardizing the whole internet and provides the guidelines for browser developers on how to correctly implement HTML, CSS, Javascript, etc. The W3 consortium has decided to take the accessibility of CAPTCHAs into consideration. This is the link to their article: http://www.w3.org/TR/turingtest/
Among the other things, the W3 consortium reports how these CAPTCHAs tests are not very effective in blocking services from real spammers: "For example, spammers can pay a programmer to aggregate these images and feed them one by one to a human operator, who could easily verify hundreds of them each hour. The efficacy of visual verification systems is low, and their usefulness is nullified once they are commonly exploited."

Is there a way to make CAPTCHAs more accessible? There are numerous blog posts and articles online that suggest alternative methods in order to make CAPTCHAs more accessible. Here are a few examples you might find interesting:

  • http://accessibility.psu.edu/captcha/ suggests using a question rather that an image or an audio file. For example, the question could be "Which animal is larger — a mouse or a horse?" or "What state is Philadelphia located in?" They also report that “it should be noted that with question-based CAPTCHA systems, hackers can develop algorithms to predict questions and answers or hire users to answer CAPTCHA questions. Rotating questions is recommended for high volume sites.”
    In my opinion this method is not strong enough, since the cultural backgrounds of the people answering those questions might not be relative to the question being posed. It is very difficult to find questions that can easily be solved by everyone, irrespective of their culture, nationality and knowledge. A potentially neutral question could be: "Is water a liquid or a solid?"

  • The American Foundation of the Blind (AFB) suggests in the following blog post a similar solution: http://www.afb.org/blog/afb-blog/can-captchas-be-made-accessible/12
    They suggest giving instructions to users, like: "Please type "hello" here." or "Please put the word "horse" in the box."

  • The National Federation of the Blind (NFB) shared this article https://nfb.org/images/nfb/publications/bm/bm09/bm0901/bm090108.htm on their website that suggests a solution on how to make the CAPTCHA feature accessible. They decided to call this new technology HIPUU (Human Interaction Proof Universally Usable).
    This is how they describe it:
    The first version of HIPUU is a combination of nontextual images and sounds. For instance, we have an image of a dog, and we have a sound clip of a dog barking. The idea being that, if you are blind, you can use the sound clip; if you have a hearing impairment or are sighted with no disability, for that matter, you can use the picture of the dog. But, because it's nontextual ”because it uses pictures and sound clips” it's actually more secure. It is more secure because image-recognition and speech-recognition technology are much better at recognizing text than at identifying pictures and certainly at identifying sounds. Humans, however, are quite adept at recognizing both graphics and sounds.
    The results are great: 100% success rate for sighted, who, by they way, liked this better than the traditional twisted-text CAPTCHAs. Blind has a 90% success rate on the first try, reaching 100% on the second. The average task-completion time was 35.2 seconds.

A team at Google has managed to develop an innovative technology that's both accessible and fulfills the purpose of identifying the user as a human or robot, and it's called: No CAPTCHA. No CAPTCHAs consists of a checkbox that simply says: "I'm not a robot". The technology involved behind this checkbox is very sophisticated and is, among other things, able to track the mouse movements around the checkbox to make sure you are a human. But the good thing is: yes, No CAPTCHA is accessible! Thanks, Google!

Here's a video that tells you more about Google's No CAPTCHAs