| Summary: | 碩士 === 朝陽科技大學 === 工業工程與管理系碩士班 === 98 === CAPTCHA, the acronym of “Completely Automatic Public Turning test to tell Computers and Human Apart”, is a security measures that guards internet against automated exploitations with abusive purposes by ill-motivated users. Among them, text-based CAPTCHA is the most common type. However, text-based CAPTCHA can be breached by character recognition programs. Therefore, to effectively tell whether a user in question is a human being or a robot program, most text-based CAPTCHA designs employ distortion techniques to defend the attack by character recognition programs. Yet, the distortion techniques themselves may increase the loading on the visual system and cognitive system of human solvers. In addition, given the trend of our aging society, the design of text-based CAPTCHA should take into account the differences between the senior and young users in terms of visual and cognitive systems. This study considered participants of two age groups (young and senior) and some common types of text-based CAPTCHA. Comparisons were made between the two groups in terms of task performance, visual fatigue, and mental workload.
The results indicated that when recognizing CAPTCHAs whose contours were incomplete due to the distortions, participants had poorer accuracy, higher visual fatigue, and higher workload; the senior group underwent more serious impact than the young group did. In addition, the senior group had higher accuracy than the young group in the recognition of CAPTCHAs that emploied color background and character distortion techniques. Therefor, this study suggests the use of distortions that do not break the character contour, extra obscure elements (such as lines or circles), and color background, in the design of CAPTCHAs to ensure the effectiveness of CAPTCHAs in terms of security and to reduce the workload real users may face when they encounter CAPTCHAs online.
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