Accessible Captcha
I installed a new extension tonight.
This extension changes the captchas from graphic words to user-definable questions and answers. The settings allow you to create up to 8 simple questions and answers that will be randomly chosen in place of the captcha. These captchas are completely accessible as long as you remember to make the questions straightforward and without cultural context (unless you need to restrict usage to a specific group or type of site visitor).