CAPTCHA

A CAPTCHA is a challenge designed to tell humans and automated programmes apart, such as typing distorted characters or selecting matching images. CAPTCHAs are a barrier for many people, particularly those with disabilities, so accessibility guidelines restrict when and how they may be required.

A visual-only or audio-only CAPTCHA excludes anyone who cannot use that sense; WCAG requires that where a CAPTCHA is used, alternative forms covering different senses are offered, or another way to prove human presence entirely - such as a behind-the-scenes risk check - is used instead.

Learn more

• Inaccessibility of CAPTCHA - the W3C note on CAPTCHA accessibility and alternatives
• WCAG