CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. It’s a common security measure to confirm a user is human, but when CAPTCHAs rely solely on visual reasoning, they’re potentially an issue for accessibility.
If you’ve encountered a prompt that asks you to “select all panels that contain a street sign" or “enter the characters below,” you’ve encountered a visual CAPTCHA.
The problem: Not all human users can perceive content visually. People with vision disabilities may use screen-reading software (or screen readers), which output text as audio or braille.
Why CAPTCHA is a Problem for Screen Readers
The major issue with CAPTCHAs is that they are typically presented as distorted images or audio clips which are often unreadable or unrecognizable to screen readers. Without being able to access the content of the CAPTCHA, screen readers cannot correctly interpret the instructions to the user.
Audio CAPTCHAs aren’t a perfectly effective alternative. Without alternative text, these tests can present problems for users with both vision and hearing disabilities — and providing alternative text would defeat the purpose of the CAPTCHA.
And some human verification methods pose problems for all users, regardless of their abilities. A Stanford study in 2010 showed that a group of 3 humans could only agree on the answer to an image CAPTCHA 71% of the time. When people can’t answer a CAPTCHA, they feel frustrated — and in many cases, they’ll leave your website.
What are the accessible alternatives to CAPTCHA?
Security measures like CAPTCHA are permitted under the Web Content Accessibility Guidelines (WCAG), provided that they include alternatives “using output modes for different types of sensory perception.”
In other words, you could use a visual CAPTCHA (or a similar verification technology), provided that you also provide an audio-based verification method.
With that said, there are accessible alternatives to classic CAPTCHA, and they’re far more effective — and easier on your users. In 2014, Google implemented reCAPTCHA v2, which requires a user to select a checkbox that states “I am not a robot.” This type of test is able to be interpreted by screen readers and is also accessible via keyboard.
reCAPTCHA v2 was an improvement, but it isn’t perfect. If the user’s behavior triggers suspicion, reCAPTCHA v2 may still provide an image or audio verification test.
In 2018, Google launched reCAPTCHA v3, which is more robust. It analyzes the user’s behavior as they browse: They’re not presented with challenges, so the experience is wholly accessible.
Don’t prioritize security above accessibility
While CAPTCHAs can be effective tools used by companies to protect their websites from malicious bots, they can also pose major barriers for individuals with disabilities.
If you’re trying to reduce spam traffic, you have options — but you don’t want to create unnecessary frustrations for your users. A few tips to keep in mind:
- If possible, use an “invisible" human verification technology. While we don’t recommend specific products, reCAPTCHA v3 is fairly standard (and more effective than reCAPTCHA v2).
- You might also consider alternatives such as hCaptcha, which uses machine learning models to detect human users.
- If your goal is to limit forum or email spam, consider using filters and bot mitigation tools instead of reasoning tests.
- Test all verification methods with a screen reader. Wherever possible, the tests should be performed by experienced screen reader users.
- Test all verification methods for keyboard accessibility. Read why keyboard accessibility is essential for digital accessibility.
- Avoid using CAPTCHAS with strict time limits. People who use assistive technologies may need more time to operate website controls, so if you must use timeouts, the user should be able to extend or pause the time limit.
Following WCAG 2.1’s Level A/AA guidelines can help you provide a better experience for people who use screen readers and other assistive technologies. The best practices of accessibility don’t limit your options for web design and development — they simply extend the same essential experience to every user.