Thesis (M.Sc.)--Chulalongkorn University, 2009

Nowadays, the internet is now becoming a part of our everyday lives. Many services, including Email, search engine, and web board on internet, are provided with free of charge and unintentionally turns them into vulnerability services. Many software robots or, in short term, bots are developed with purpose to use such services illegally and automatically. Thus, web sites employ human authentication mechanism called Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) to counter this attack. Unfortunately, many CAPTCHA have been already broken by bots and some CAPTCHA are difficult to read by human. In this thesis, a new CAPTCHA method called 3D CAPTCHA is proposed to provide an enhanced protection from bots. This method based on the assumption that human can recognize 3D character image better than automated program bots. Moreover, this thesis also introduces the 3D - animation CAPTCHA method to increase protection from bots. This method includes multiple image frames instead of using a single frame found in general CAPTCHA