reCaptcha is a very popular CAPTCHA system on the Internet. Due to its design, we find that reCaptcha figures have certain feature that can potentially weaken this system. This paper discussed the design of reCaptcha, and use some simple Machine Learning algorithm to find a way to tell the difference between “control word” and “unknown word”. We also designed the experiment to evaluate our hypo...

CAPTCHAs have been deployed ubiquitously by web sites to combat automated malicious programs. Security against web bots and usability to legitimate users are two main goals that have to be simultaneously satisfied when designing a useful CAPTCHA scheme. However, there exists a well-known and intricate trade-off between these goals. So far, balancing this trade-off remains an art rather than a s...

Segmentation subdivides a CAPTCHA image into its constituent regions or objects. The point to which the subdivision is carried depends on the problem being solved. That is, segmentation should end when the objects of interest inan application have been isolated. Without a good segmentation algorithm, an object may never be identifiable. Image segmentation continues to be an vital and active res...

As a result of continuing advances in computer capabilities, it is becoming increasingly difficult to distinguish between humans and computers in the digital world. We propose using the fundamental human ability to distinguish between things that are aesthetically pleasing and those that are not as the basis of a method to verify that a communicating party is human. We discuss one possible impl...

Spam over internet telephony (SPIT) refers to all unsolicited and massive scale attempts to establish voice communication with oblivious users of voice over internet protocol (VoIP) services. SPIT exhibits a significant increase over the last years, thus developing into a serious threat with adverse impact and costs for the business economy. An audio completely automated public Turing test to t...

This paper studies reverse Turing tests to tell humans and computers apart. Contrary to classical Turing tests, the judge is not a human but a computer. These tests are often called Completely Automated Public Turing tests to tell Computers and Humans Apart (CAPTCHA). The main purpose of such test is avoiding automated usage of various services, preventing bots from spamming on forums, securing...

Audio CAPTCHA systems, which distinguish between software agents and human beings, are especially important for persons with visual disability. The popular approach is based on mixing-based methods (MBM), which use the mixed sounds of target speech and noises. We have proposed a deletion-based method (DBM) which uses the phonemic restoration effects. Our approach can control the difficulty of t...

In an on-line transaction, a client usually have to present some authenticators (password, user certificate or both) to the server. However, those authenticators are exposed to client-side malware such that the malware is able to obtain the server-client messages, or impersonate the user to build another “secure” channel with the server. The present paper aims to patch this client-side security...

The Complete Automatic Public Turing test to tell Computers and Humans Apart (CAPTCHA) is a modern implementation of the Turing test. A CAPTCHA asks a series of questions which are supposed to be relatively easy for mature human beings but hard for machines to answer. A CAPTCHA, as its name suggests, is generally used as a tool to distinguish human beings from machines when the corresponding pa...