How to tell legitimate users apart from automated systems in an accesible way has been a problem for developers of accessible web sites for a long time. Here at Visits Unlimited we use invisible systems on comment, contact and log in forms that minimise the risk of causing accessibility problems but even these can cause problems on occasion.
Raghavendra Satish Peri has written an interesting article at digitala11y.com discussing different methods, their advantages and disadvantages, and problems on the methods used by very large sites.
…I wanted to contribute to the accessibility pages on Wikipedia recently and decided to make an account. I thought the process would be easy to register and start making edits, but I was quickly proved wrong. It requires solving a CAPTCHA.
I thought there might be an alternative method to complete my registration, but the whole exercise to find an alternative on Wikipedia frustrated me. In fact, I never found an alternative that day that used audio or a one-time confirmation code sent to a mobile device.
This is what it’s like to be a visually impaired person who uses the internet. Even the world’s most popular sites aren’t completely accessible.
You can read the full article on Digital A11Y’s accessibility blog here.