Skip to content

CAPTCHA: A Digital Puzzle and Accessibility Challenge

Have you ever found yourself staring at a CAPTCHA, squinting and tilting your head, trying to decipher the distorted letters or images? CAPTCHAs are notoriously inaccessible. So why do so many websites use them? And how can they be made more accessible?

In this blog post, we’ll examine CAPTCHAs and why they are needed, the barriers they present to people of varying abilities, and how we can take a more deliberate approach to designing CAPTCHAs that are easier to interact with.

What is CAPTCHA?

CAPTCHAs are designed to distinguish human users from automated bots as a security measure to prevent bots from accessing websites. CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart.

The Accessibility Challenges of CAPTCHA

CAPTCHAs pose significant barriers for users with disabilities, as they are not designed to accommodate diverse user needs.

Visual Challenges

CAPTCHA can pose significant challenges for screen reader users and individuals with visual impairments like color blindness and low vision. For instance, consider the CAPTCHA below. Portions of each turquoise letter are obscured by black lines, making them difficult to discern against the white background. While the contrast between the letter color and the black lines meets WCAG standards (11.07:1), the contrast between the letters and the white background falls short (1.89:1). This means that parts of the letters may be effectively invisible to users with specific visual impairments. Additionally, bright lighting conditions, like bright sunlight, can further complicate these visibility issues, making it nearly impossible to complete the CAPTCHA task.

Rectangle shape with a white background and black, vertical line. Turquoise colored letters are placed horizontally across the rectangle with portions of each letter hidden behind a black line.

For an image-based CAPTCHA, you must include ALT text that informs the user of its purpose. In addition, if there is an alternative CAPTCHA, like audio, this must be conveyed in either the ALT text of the image CAPTCHA or the surrounding text.

Auditory Challenges

Audio CAPTCHAs can be more complicated than visual CAPTCHAs. Screen readers tend to talk over the audio CAPTCHA as they read the characters, making it difficult for the user to hear the CAPTCHA clearly. In addition, audio quality can be poor, or background noises can make it difficult to decipher the spoken letters or numbers in the CAPTCHA. Hear an example of an audio CAPTCHA. (YouTube)

Cognitive Challenges

CAPTCHAs that involve problem-solving, like math equations, identifying ambiguous images, or solving puzzles, can be frustrating for people with cognitive impairments. Adding a time limit to these CAPTCHAs can also be challenging and increase cognitive load.

Mobility Challenges

CAPTCHAs that require precise mouse movements, typing of mixed case letters with numbers, and / or have target sizes that do not meet WCAG standards pose extreme difficulties for those with mobility impairments who use keyboard-only navigation or other mobility-related assistive devices.

There are more advanced CAPTCHA technologies that "use AI-driven behavioral and risk analyses to authenticate human users based on activity patterns rather than a single task." ~ What is CAPTCHA, IBM

The challenge with this CAPTCHA technology is that it can inadvertently report a false positive, identifying someone who uses assistive technologies as a bot since their website navigation patterns do not ordinarily fit ‘typical’ user navigation profiles.

Creating Accessible CAPTCHAs

  • Clear instructions: Provide clear and concise instructions in plain language for completing CAPTCHA challenges. Make sure the instructions are in text only - no images of text. And label any input fields clearly.
  • Error messaging: Provide clear, easy-to-understand error messages that help users complete CAPTCHA challenges correctly.
  • Text-based CAPTCHA options: Offer text-based CAPTCHA alternatives for users who cannot interpret images or have cognitive difficulties.
  • ALT Text: For image-based CAPTCHA, use ALT text that informs the user of its purpose and / or informs the user of an alternative CAPTCHA.
  • Audio descriptions: To assist users with visual impairments, consider adding audio descriptions for CAPTCHA images. Be sure to produce high-quality sound with no background noise.
  • Adjustable time limits: Allow users to adjust CAPTCHA time limits to accommodate users with cognitive or motor impairments.
  • Contrast: Visual components of CAPTCHAs or any alternative authentication methods should comply with WCAG color contrast requirements.
  • Keyboard-only accessible: Make sure all interactive elements of the CAPTCHA are accessible by keyboard or other non-mouse technology.

As stated in the first paragraph of this blog post, CAPTCHAs are notoriously inaccessible. For that reason, it's recommended to avoid using CAPTCHAs whenever possible and explore alternative authentication methods that do not require human input, such as biometrics.

If you must use CATACHAs, create them using the accessibility guidelines presented here or explore more accessible alternatives like Google’s reCAPTCHA technology.

Resources

Maggie Vaughan, CPACC
Content Marketing Practitioner
DubBot