探討年齡對文字驗證碼工作之影響

Study of age-related effects on the performance of text-based CAPTCHA tasks

徐志翔(Jhih-Siang Syu)

指導教授 ： 李英聯

朝陽科技大學/理工學院/工業工程與管理系/碩士(2010年)

摘要

驗證碼(Completely Automated Public Turing test to Tell Computers and Humans Apart, CAPTCHA)是一種預防惡意使用者利用自動機器人程式濫用網路服務的安全措施，其中又以文字型態的驗證碼最為普遍；然而文字型態的驗證碼仍可透過電腦程式加以辨識而破解。因此驗證碼的設計均透過不同的干擾設計，使電腦不易辨識，以達到區分使用者是電腦還是人類的目標，但過度的干擾設計可能會增加人類在辨識時視覺與認知的負荷。此外，隨著社會高齡化的趨勢，中老年族群網路使用者日益增加，文字驗證碼的設計更需考量該族群在視覺及認知方面與其它族群的差異。因此本研究將年齡族群分別為青少年和中老年，比較年齡族群和干擾設計在辨識文字驗證碼時，文字驗證碼績效、視覺疲勞及心智負荷量等方面的差異。

實驗結果顯示，受測者在辨識字體破碎及不完整的干擾類型時，辨識績效較差，且視覺疲勞及心智負荷量都較高，其中又以中老年族群受到的影響最為嚴重。此外，中老年族群在辨識彩色背景與文字搭配的干擾設計時有頗高的成功率。因此，本研究建議使用不會破壞字體完整性的干擾設計，並增加遮蔽元素(如線條、圓圈等)及搭配彩色背景，如此除了可有效防止文字驗證碼被破解外，又能減少使用者在辨識文字驗證碼時所面臨的負荷。

關鍵字

年齡 ； 驗證碼 ； 工作負荷 ； 視覺疲勞 ； 光學文字辨識

並列摘要

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.

並列關鍵字

CAPTCHA ； age ； OCR ； visual fatigue ； workload

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