A CAPTCHA is a test that is used to determine whether or not a user is human. CAPTCHAs often takes the form of a distorted image containing a sequence letters or numbers that the user is asked to identify and type into an input field. They are commonly used on webpage forms to verify the authenticity of the information being submitted. CAPTCHAs pose a very difficult problem for accessibility because any attempt to clarify the CAPTCHA for the benefit of people with disabilities may make the CAPTCHA easier for computers to process and negate its very purpose. Therefore, the alternative text description of a CAPTCHA image should inform the user of the purpose of the image and direct them to an alternative, accessible version. This will often be an audio CAPTCHA that does not rely upon visual identification.
If possible, avoid using visual CAPTCHAs to verify users. However, if a CAPTCHA must be used, then ensure that the alt attribute of the image contains an explanation of the CAPTCHA and directs the user towards an alternative, accessible version.
No example is available.