Are you a Human or Robot? or Everything CAPTCHA Revati Ghadge #1 , Archana M. Naware #2 #1 Master of Computer Applications (M.C.A.), Lokmanya Tilak College of Engineering, Sector 4, Koparkhairane, Navi Mumbai-400709, India #2 Department of Computer Engineering, Lokmanya Tilak College of Engineering, Sector 4, Koparkhairane, Navi Mumbai-400709, India Abstract— CAPTCHA stands for Completely Automated Public Turing test to tell Computer and Humans Apart. CAPTCHAs are used to improve the security of Internet based applications in order to ensure that a web based application which is intended to be used by a human being is not maliciously used by Artificially Intelligent programs called bots. Bot is a simple computer program used to perform highly repetitive operations. Anti- CAPTCHA technology is advancing, and so are attempts made to build a better CAPTCHA or its equivalent. As the current CAPTCHA methods are striving to be more difficult for bots, they are gradually becoming difficult and annoying for human users as well, and this is the main drawback of CAPTCHA. The applications that use CAPTCHA need to be aware and up to date about reliability of the CAPTCHA they are using. A CAPTCHA system is considered to be broken if an automated attacker reaches a precision of 1%, as it fails the main purpose. To ensure security of the web based applications, users have to prove if they are human or not. Keywords— CAPTCHA, Turing Test, BOT, Usability, Security, CAPTCHA Alternatives. I. INTRODUCTION We often use your computer for website registration, email services, online ticket booking or online voting. However, before the users can move forward with our task, they first have to pass a test. It's not a hard test -- and that's the point. For humans, the test should be simple and straightforward. But for a bot, the test should be almost impossible to solve. This sort of test is a CAPTCHA, also known as a type of Human Interaction Proof (HIP). Users come across CAPTCHA tests on lots of Web sites. The most common form of CAPTCHA is an image of several distorted letters. CAPTCHA was invented in 2000 at Carnegie Mellon University (CMU) by Luis Von Ahn, Manuel Blum, Nicholas J. Hooper and John Langford. CAPTCHA technology has its foundation in an experiment called the Turing Test. Alan Turing, known as father of modern computing, proposed the test as a way to examine whether or not machines can think or appear to think like humans. The classic test is a game of imitation, having two participants. One of the participants is a machine and the other is a human. The interrogator can't see or hear the participants and has no way of knowing which is which. If the interrogator is unable to figure out which participant is a machine based on the responses, the machine passes the Turing Test [1]. The goal of CAPTCHA, is to create a test that humans can pass easily but machines cannot. It is also important that the CAPTCHA application is able to present different CAPTCHAs to different users. If a visual CAPTCHA presented is same for every user, a spammer will spot the form, decipher the letters and will program an application to type in the correct answer automatically. Who Uses CAPTCHA? CAPTCHAs are mainly used by websites that offer services like online polls and registration forms. Web-based email services like Gmail, Yahoo and Hotmail offer free email accounts for their users. On each sign-up process, users will come across a CAPTCHA at the end of the sign-up form so as to ensure that the form is filled out only by a legitimate human and not by a computer bot. CAPTCHAs are used to prevent spammers from using a bot to generate hundreds of spam mail accounts [2]. II. TYPES OF CAPTCHA CAPTHCAs mean presenting a challenge response test to the users. Most commonly used, following are the types of captcha: 1. The Standard Distorted Text CAPTCHA with an Audio Option Figure 1. Distorted Text CAPTCHA It is reliable, but some of the distorted word images are rather hard to solve. To get past that it allows you the option to “reCaptcha”, in order to receive a new one. There is also an audio option if you are unable to visually make out the word. 2. Picture Identification Captcha Figure 1. Picatcha This CAPTCHA provides the user with a choice of choosing the correct image that they are asked to identify. Revati Ghadge et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 6 (3) , 2015, 2800-2805 www.ijcsit.com 2800