One alternative to using a visual CAPTCHA is to ask a simple question, such as "What is 2 + 2" or "On a hot day, is it hot or cold?". Humans should be able to answer the question but it is unlikely that a computer will be able to. Be careful of making the questions too difficullt however, as this may exclude certain users. Another alternative is to use an audio CAPTCHA, which typically presents an audio file containing information that the user must enter into the form. Wherever a visual CAPTCHA is provided, an accessible alternative should be provided as well as a clear link to the alternative.
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.