Is CAPTCHA Section 508 compliant?
CAPTCHA is as Section 508 compliant as you make it to be. It can certainly be done. In this post we will review those Section 508 standards which are relevant when creating a CAPTCHA solution. At this point, we will only concentrate on the current Section 508 standards, not on the proposed recommendations, as they may change before they legally become effective.
Section 508 requires to provide a text equivalent for non-text elements. This itself defeats the purpose of an only image based CAPTCHA, because if you provide a text alternative, automated systems can easily pass through your challenge. So, while it is ok to use an image based CAPTCHA, you will need some kind of an alternative.
It is a very popular solution to provide an audio CAPTCHA, where the users can activate a link which will announce the content of the image. This itself brings it much closer to accessible to many people, however, keep in mind that it is not suitable for people with learning disabilities, or to deaf blind people.
Section 508 also requires equivalent alternatives for multimedia presentations, which include audio CAPTCHA as well. So, while the audio CAPTCHA opened doors to many more people, in reality, it still does not make your solution Section 508 compliant.
Another consideration when using an image based CAPTCHA is that it cannot provide the image by the use of a style sheet. Section 508 requires that pages should be readable without an associated style sheet. Once somebody disables your style sheet, the image CAPTCHA will be useless.
Your only Section 508 compliant solution will be a challenge question, which users have to answer. It could be a simple math equation, a question which is common knowledge to all people, though it is debatable, but not to robots. However, you will have to ensure that you comply with the Section 508 form requirements. Attach labels to the fields programmatically, and make sure that the fields can be accessed by keyboard only. In addition, provide clear instructions on solving the challenge question.
For ideas on creating a CAPTCHA which is not image based, read accessible alternatives for CAPTCHA.