Advanced character collage captcha

Abstract

Text based CAPTCHA systems are widely used as a security mechanism for web access control. Considering their broad use, many attacks are challenging them every day. Most of the attacks aimed at CAPTCHAs are based on the latest computer vision techniques, AI methods and OCRs, so it is imperative to enhance these methods even more. There are number of proposals for CAPTCHA security, but it is hard to achieve a good balance between CAPTCHA practicality and its security. Advanced Character Collage CAPTCHA is a highly random novel method which uses the strengths of unbroken CAPTCHAs along with the weaknesses of present ones, and relies on imperfection of computer vision techniques. The proposed CAPTCHA is generated through a series of unique creation steps, each of them implementing carefully analyzed features in order to increase human recognition rate, and at the same time, to reduce computer recognition rate. The degree of recognition within the proposed method is evaluated using several tests, while its readability by humans is tested through two surveys.