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...

CAPTCHA stands for Completely Automated Public Turing Test to Tell Computer and Human Apart. It is the test that human can pass easily but computer cannot. For example, humans can read distorted text, but current computer programs cannot. For many years, CAPTCHAs have proven very useful for many reputable, Web-based email and application service providers, including social networking sites and ...

We present a black-box attack against an already deployed CAPTCHA that aims to protect a free service delivered using the Internet. This CAPTCHA, referred to as ‘‘Math CAPTCHA’’ or ‘‘QRBGS CAPTCHA’’, requests the user to solve a mathematical problem in order to prove human. We study significant problems both in its design and its implementation, and how those flaws can be used to completely sol...

“CAPTCHA” stands for Completely Automated Public Turing Test[1] to Tell Computers and Humans Apart[2]. Due to exponential growth of internet, security of web application has become a vital issue and many web applications facing a threat of web bots also known as internet Robot is an automated script which executes over the web forms and occupy web spaces and thus increases network traffic. The ...

This paper studies the effect of individual differences on user performance related to text-recognition CAPTCHA challenges. In particular, a text-recognition CAPTCHA mechanism was deployed in a three-month user study to investigate the effect of individuals’ different cognitive processing abilities, targeting on speed of processing, controlled attention and working memory capacity toward effici...

CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” and has received much attention since it first began appearing on websites. It requires the deciphering of distorted texts, mostly in English which is something that computers still cannot do well. It is also helpful in preventing the abuse of online services. The current text-based CAPTCHA requires ...

CAPTCHA is now commonly used as standard security technology to tell computers and humans apart. The most widely deployed CAPTCHAs are text-based schemes. In this paper, we document how we have broken such a text-based scheme which uses the “connecting characters together (CCT)” principle. CAPTCHAs of this type can be classified into three types: CAPTCHA with overlap but no noise arcs; CAPTCHA ...

In this paper the elements of the CAPTCHA usability are analyzed. CAPTCHA, as a time progressive element in computer science, has been under constant interest of ordinary, professional as well as the scientific users of the Internet. The analysis is given based on the usability elements of CAPTCHA which are abbreviated as user-centric approach to the CAPTCHA. To demonstrate it, the specific typ...

The Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) is used to believe that a human is using the web service [1]. For the online services which are been provided in web services is been abused by automated bots over the internet. So CAPTCHA is used as a protection from these malicious programs for web security. But the bots are intelligent enough to break th...