Secure and Easy to Read Automated Handwritten CAPTCHA

Abstract

Time has changed, now humans have to pass a test against computer generated spam bots; called CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart). The automated scripts, spam bots and robots of web portals can bring down a running website in few minutes. Most of the time the new account creation or online polling suffers from this issue. CAPTCHA is an automated test based on recognition tasks that are easy to pass for human and difficult for current computers to pass. In this paper the recognition difficulty of handwritten text by an OCR is used as a key for secure CAPTCHA formation. The use of numeric and case sensitive letters make the range of possible guesses computationally very large. The application of random image alteration techniques such as noise, color of letters, appearance of letters, length of word etc make the characters more difficult to recognize by current set of OCRs but still relatively easy and readable for a human to respond.