Algorithm for Secured Online Authentication Using CAPTCHA

CAPTCHA stands for Completely Automated Public Turing Tests to Tell Computers and Humans Apart. A CAPTCHA is a program that protects websites against bots -automated scripts by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text but current computer programs can´t. The threats from bots is growing rapidly and also increasing in technical sophistication causing various types of attacks. These attacks are affecting social aspects of human beings. Human being or legitimate users are cheated by false requests disturbing their social life. This paper aims to provide secured authentification by verifying strength of CAPTCHA. The strength of CAPTCHA can be verified by solving it. The CAPTCHA solving has mainly three steps such as preprocessing, segmentation and character recognition. The input distorted image of CAPTCHA is passed through preprocessing module which removes noise and gives raw image which is then segmented. These segmented characters are recognized using pattern-matching technique achieving 88% accuracy. The result shows that this algorithm provides secured social relevance to avail free Internet services and in turn improve usability of well-claimed CAPTCHA.