Abstract
A CAPTCHA is used to automatically differentiate between human users and automated software to prevent bots from accessing unauthorized websites. Most proposed CAPTCHAs are not accessible to visually impaired users because of the memorability of the CAPTCHA's numerical digits. Recalling six random spoken digits is a difficult task for any human. Visually impaired users must typically play the audio several times to memorize the spoken digits in the correct order. The authors reviewed existing CAPTCHAs for visually impaired users and concluded that the high cognitive load is more susceptible to response errors due to extensive challenge digits intended for visual users. Thus, the authors proposed a novel method that improves current audio CAPTCHA by enhancing the display of the challenge and improving the memorability of its phraseology. The proposed CAPTCHA presents short common phrases, such as "piece of cake. " After hearing or seeing the phrases, the users are required to type the first letter of each word from the presented phrases, such as POC for a piece of cake. The study results of 11 visually impaired users concluded that the memorability and success rate for the IRemember CAPTCHA was 82.72%, compared to the audio CAPTCHA at only 48.18%. It has also demonstrated higher memorability and less workload than the traditional audio method. This research indicates that using common knowledge and experience in the design process for a CAPTCHA method for these users can enhance performance and minimize workload and, hence, error rates.