An Orientation based Image CAPTCHA
Yashwanth Chanamolu · OhioLink ETD Center (Ohio Library and Information Network) · 2009
CAPTCHA is now almost a standard security technology, and has found widespread application in commercial websites.To date, almost all CAPTCHA designs are labeling based.Labeling based CAPTCHAs refer to those that make judgment based on whether the question "what is it?"has been correctly answered.Essentially in Artificial Intelligence (AI), this means judgment depends on whether the new label provided by the user side matches the label already known to the server.Labeling based CAPTCHA designs have some common weaknesses that can be taken advantage of attackers.First, the label set, i.e., the number of classes, is small and fixed.Due to deformation and noise in CAPTCHAs, the classes have to be further reduced to avoid confusion.Second, clean segmentation in current design, in particular character labeling based CAPTCHAs, is feasible.Sometimes, it is even trivial.The state of the art of CAPTCHA design suggests that the robustness of character labeling schemes should rely on the difficulty of finding where the character is (segmentation), rather than which character it is (recognition).However, the shapes of alphabet letters and numbers have very limited geometry characteristics that can be used by humans to tell them yet are also easy to be indistinct.The major contribution of this thesis is that we propose a new direction in CAPTCHA design by focusing on orientation rather than labeling.We introduce an orientation based image CAPTCHA which uses an image set which gets dynamically updated.By focusing on orientation we eliminate problems facing labeling based CAPTCHAs like limited iii label classes and object recognition.We built a CAPTCHA web application using Java Sever Pages technology and used AJAX techniques to make the user interface more interactive and user friendly.We deployed our application on a web server and tabulated the response time and success ratio results we got.iv This is dedicated to my parents v ACKNOWLEDGEMENTS I would like to thank my advisor Dr. Dong Xuan for the guidance and the intellectual support he has