Mitigating the accessibility cost of CAPTCHA
CAPTCHA is the most effective anti-spam technique in use today, because it acts as a preventative whereas other techniques detect likely spam and shunt it into a queue for moderation, they still allow the spam to get through. However this effectiveness comes at a heady price – seriously diminishing the accessibility of your website.
By taking some simple and sensible steps, we can mitigate this and partially restore accessibility.
The first option is to stop using image-based CAPTCHAs. There are a number of logic and maths based versions available which are much more accessible.
Another way is to provide a refresh button for the CAPTCHA. This must not be recorded as an attempt at answering. Most popular CAPTCHA implementations are session based and work by recording the number of submits. A simple link to the same page will work effectively, but this will discard any data the user has entered. Therefore we should use a submit button and return the submitted values along with a new test.
The final way is to provide an alternative way to allow users to register with/comment on your site. Going into details of specific systems is beyond the scope of this article, but most systems have some method of flagging registrations/comments for attention. These are then put into a queue to wait for the approval of the site administrator. By flagging registrations/comments that have been made through the accessible gateway, we can provide a way to both protect from the vast majority of spam and allow users to register/comment on your site.