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Evaluating Existing Audio CAPTCHAs and an Interface Optimized for Non-Visual Use - aravind anilkumar - 10-04-2017 Evaluating Existing Audio CAPTCHAs and an Interface Optimized for Non-Visual Use [attachment=657] INTRODUCTION AND MOTIVATION The goal of a CAPTCHA1 is to di erentiate humans from automated agents by requesting the solution to a problem that is easy for humans but di cult for com- puters. CAPTCHAs are used to guard access to web re- sources and, therefore, prevent automated agents Making CAPTCHAs Accessible Audio CAPTCHAs were introduced soon after their vi- sual alternatives [22, 9], and have been slowly adopted by web sites using visual CAPTCHAs since that time. Although the adoption of audio CAPTCHAs has been slower than that of visual CAPTCHAs, many popular sites now include audio alternatives, including services o ered by Google and Microsoft. Over 2600 web users have signed a petition asking for Yahoo to provide an accessible alternative [25]. The reCAPTCHA project, a popular, centralized CAPTCHA service with the goal of improving the automated OCR (Optical Character Recognition) processing of books also provides an audio alternative. Although audio CAPTCHAs exist, their usability has not been adequately examined. Other Alternatives Because audio CAPTCHAs remain di cult to use and are not o ered on many web sites, several alternatives have been developed supporting access for blind web users. Many sites require blind web users to call or email someone to gain access. This can be slow and de- tracts from the instant grati cation a orded to sighted users. The WebVisum Firefox extension enables web users to submit requests for CAPTCHAs to be solved, which are then forwarded to their system to be solved by a combination of automated and manual techniques [24]. Because of the potential for abuse, the system is currently o ered by invitation only and questions re- main about its long-term e ectiveness. For many blind web users the best solution continues to be asking a sighted person for assistance when required to solve a visual CAPTCHA. Targeting Non-Visual Access The interface that we developed for solving audio CAPT- CHAs builds on work considering the development of non-visual interfaces. Such interfaces are often very dif- ferent than the interfaces developed for visual use even though they enable equivalent interaction. For instance, in the math domain, specialized interfaces have been developed to make navigation of complex mathematics feasible in the linear space exposed by non-visual inter- faces [16]. Emacspeak explores the usability improve- ment resulting from applications designed for non-visual access instead of being adapted from visual interfaces [17]. EVALUATION OF EXISTING CAPTCHAS Many web services now o er audio CAPTCHAs because they believe them to be an accessible alternative to vi- sual CAPTCHAs. However, the accessibility and us- ability of these audio CAPTCHAs has not been exten- sively evaluated. Our initial study aims to evaluate the accessibility of existing audio CAPTCHAs and search for implications we could use to improve them. We did this by gathering currently used CAPTCHAs from the most popular web services and presented them to study participants to solve. During the study, we col- lected tracking data to investigate the means by which both sighted and blind users solve CAPTCHAs. The tracking data we collected allowed us to analyze the timing (from page load to submit) of every key pressed and button clicked, and search for problem areas and possible improvements to existing CAPTCHAs. Results Of our 162 participants, 89 were blind and 73 were sighted; 56 were female, 99 were male, and 7 chose not to answer that question; and their ages ranged from 18 to 69 with an average age of 38.0 (SD = 13.2). Before participating in our study, blind and sighted participants showed di ering levels of frustration to- ward the audio and visual CAPTCHAs they had al- ready come across. Participants were asked to rate the following questions on a scale from Strongly Agree (1) to Strongly Disagree (5) or opt out by answering \I have never independently solved a visual[audio] CAPT- CHA" for the following questions: \Audio CAPTCHAs are frustrating to solve." and \Visual CAPTCHAs are frustrating to solve." |