for his invaluable guidance, support, time, and understanding (and tolerance) this past year. Lastly, I thank my parents for their perseverance in dealing with me for the last 24 years. It really is quite a feat.

CAPTCHAs are known as Captcha which stands for Completely Automated Public Turing test to tell Computer and Human Apart. used prevent automated scripts from harvesting email addresses publicly accessible forms on the internet submitting them spammers. mostly utilised because computers have a difficult time deciphering text concealed behind distorted visuals, but humans an easier information hid...

-------------------------------------------------------------ABSTRACT-------------------------------------------------------A novel technique of Captcha is regenerated by using composite images that are generated in the given data base. Captcha is a type of challenge response test used in computing to determine whether or not the user is human. Captcha are used to prevent bots or automated prog...

Abstract CAPTCHA ( Completely Automated Public Turing test to tell Computers and Humans Apart ) has long been used keep automated bots from misusing web services by leveraging human-artificial intelligence (HAI) interactions distinguish whether the user is a human or computer program. Various schemes have proposed over years, principally increase usability security against emerging hackers perf...

Since their inception, captchas have been widely used for preventing fraudsters from performing illicit actions. Nevertheless, economic incentives have resulted in an arms race, where fraudsters develop automated solvers and, in turn, captcha services tweak their design to break the solvers. Recent work, however, presented a generic attack that can be applied to any text-based captcha scheme. F...

It is an interesting problem how a human can prove its identity to a trustworthy (local or remote) computer with untrustworthy input devices and via an insecure channel controlled by adversaries. Any input devices and auxiliary devices are untrustworthy under the following assumptions: the adversaries can record humans’ operations on the devices, and can access the devices to replay the recorde...

The research presented in this thesis aims to extend the capabilities of human interaction proofs in order to improve security in web applications and services. The research focuses on developing a more robust and efficient Completely Automated Public Turing test to tell Computers and Human Apart (CAPTCHA) to increase the gap between human recognition and machine recognition. Two main novel app...