Survey of Different Types of CAPTCHA Ved Prakash Singh, Preet Pal School of Computer Science, Lovely Professional University Phagwara, Punjab Abstract— CAPTCHA is an acronym for Completely Automated Public Turning Test to tell Computers and Humans Apart [1]. CAPTCHA is basically used as a protection from these malicious programs like Bot. Now a day’s for web security we are using different type of captcha. In this paper we describe all type of captcha and also describe their drawbacks all type of captcha. We also describe application of captcha. And review paper of different types of Captcha. Index Terms—CAPTCHA, BOT, Turing Test, Security, HIP OCR. I. INTRODUCTION First time CAPTCHA was invented in 2000 at Carnegie Mellon University by John Langford, Nicholas J. Hooper and Luis Von Ahn [1]. CAPTCHA is an acronym for “Completely Automated Public Turning Test to tell Computers and Humans Apart” [2]. The progress of Internet, Web security has become an important issue. There are too many malicious threats across the Internet which may compromise your system in the absence of any secure application which provides protection against such threats. One such threat is the Bot. A Bot is a malicious program which has the capability to run automated tasks over the network and thus creating problem in the network [3]. CAPTCHA is one such shield which can be used as a protection from these malicious programs like Bot. A CAPTCHA may come in various forms like text based or image based CAPTCHA. The Bot operation is similar to reverse “TURING TEST” (given by Alan Turing) [2] where the program acts like judge and the other person acts like user. If the user fails this test then he/she is considered to be a machine otherwise the user is considered to be an authentic user or a human being. CAPTCHA is a defensive system that acts as a tool to check web Bots from exploiting online services on the internet including free email providers, wikis, blogs etc. It is a HIP system that is widely used to secure the internet based applications. It is also called as a challenge response test which gives a challenge to the users, when the user gives correct answer he is considered as human otherwise a web bot. CAPTCHA is an authentication process based on challenge-response authentication. CAPTCHA provides a mechanism with the help of which a user’s can protect themselves for spam and password decryption by taking a simple test. In this test a user will see either an image or a text which are normally distorted. The user is supposed to enter the pattern exactly as shown to him if the CAPTCH is based on text. If the CAPTCHA is based on image the user is supposed to enter the correct name of the image which correctly symbolizes the image. CAPTCHA is used where authenticated access is the primary concern. Various web services like Yahoo, Google, and Bing etc. use CAPTCHA to differentiate between an authenticated user and a malicious program. CAPTCHAs are also used in the sites which provide access to sensitive data, such credit card accounts and banks. II. CATEGORIES OF CAPTCHA CAPTHCAs means presenting a challenge response test to the users or humans. They are classified based on what is distorted that is whether characters, digits, or images. Some types of CAPTCHAs are given below: 1. CAPTCHAs based on text. 2. CAPTCHAs based on image. 3. CAPTCHAs based on audio. 4. CAPTCHAs based on video. 5. CAPTCHAs based on puzzle. 1) CAPTCHAs based on text: Text based CAPTCHAs is a very simple to implement. It is very effective and requires a large question bank. In Text based captcha the Number of classes of characters and digits are very small so the problem occur for user to identify the correct characters and digits. The text based captcha is possible to identify the character and digit through Optical character recognition (OCR) technique [2, 4]. In Text based CAPTCHAs simple asked questions like as based on arithmetic equation some example are given below: A) What is three plus two (3+2=?). B) What is six minus one (6-1=?). C) Which of cabbage, apple and table is vegetable? Example of text based CAPTCHA. Fig 1: Text Based Captcha 2) CAPTCHAs based on image: Graphics-based CAPTCHAs are challenge-tests in which the users have to guess those images that have some similarity. For example: visual puzzles. In image based CAPTCHAs user is required to identity image. The advantage of image based Ved Prakash Singh et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 5 (2) , 2014, 2242-2245 www.ijcsit.com 2242