CAPTCHA is standard for providing security for web services. It mainly used to avoid Denial-Of –Service attack. CAPTCHA Completely Automated Public Turing Test to Tell Computers and Humans Apart or it is designed to distinguish automatic bots and human. Many different CAPTCHA were introduced and it is in use. All the CAPTCHA have some disadvantage. Textbased CAPTCHA can be easily identified by ...

Captcha (Completely Automated public Turing test to tell Computers and Humans Apart) system is used to verify whether a user is human or computer program. It’s also known as human Interactive Proof (HIP) and based upon Artificial Intelligence. Captcha is a program that protects websites from web-bots by generating tests that computer cannot pass but human can pass .This paper comprise introduct...

In this paper, we firstly introduce that CAPTCHA technology development and the various type of reading CAPTCHA, sound CAPTCHA, graph CAPTCHA at present. The second, we build one kind of the Chinese CAPTCHA model. The third, a new Chinese CAPTCHA system based on AJAX is proposed, which proceed to generate character characteristic based random problem and answer. On its performance, we show that...

CAPTCHAs are a standard security mechanism used on many websites to protect online services against abuse by automated programs, or bots. The purpose of a CAPTCHA is to distinguish whether an online transaction is being carried out by a human or a bot. Unfortunately, to date many existing CAPTCHA schemes have been found to be vulnerable to automated attacks. It is widely accepted that state-of-...

A Captcha is a puzzle that is easy for humans but hard to solve for computers. A formal framework, modelling Captcha puzzles (as hard AI problems), was introduced by Ahn, Blum, Hopper, and Langford ([ABHL03], Eurocrypt 2003). Despite their attractive features and wide adoption in practice, the use of Captcha puzzles for general cryptographic applications has been limited. In this work, we explo...

CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) is a simple test that is easy for humans but extremely difficult for computers to solve. CAPTCHA has been widely used in commercial websites such as web-based email providers, TicketMaster, GoDaddy, and Facebook to protect their resources from attacks initiated by automatic scripts. By design, CAPTCHA is unable...

This paper discusses and demonstrates the interplay between system security and user interface convenience in CAPTCHA design, and in particular, mobile device CAPTCHA design. A CAPTCHA is a computer-based security test used to distinguish human users from artificial users, preventing automated abuse of networked resources. As mobile network services improve, we can anticipate that future mobile...

CAPTCHAs have become a very popular security mechanism used to prevent automated abuse of online services intended for humans. Different flavors of CAPTCHA can be seen on Internet. However, a wide variety of CAPTCHAs have been successfully attacked by automated programs. This has made CAPTCHA design an interesting area for research. Among various flavors of CAPTCHA text based are most preferabl...

To distinguish between human user and computer program to enhance security, a popular test called CAPTCHA is used on Web. CAPTCHA has an important role in preventing Denial Of Service (DOS) attacks in computer networks. There are many different types of CAPTCHA in different languages. Due to the expansion of Persian-language and documents on internet, creating a suitable Persian CAPTCHA seems t...

Currently, it is unavoidable of typing CAPTCHA (Completely Automated Public Turing test to tell Computer and Human Apart) before accessing to the Internet. This technique mostly can distinguish bots from human being. Thus, the system is protected from any unwanted persons or programs. There are various researches proposed several of CAPTCHA techniques to protect bots. These are such as Text-bas...