Advanced Collage CAPTCHA

Some Internet Web sites for providing services to their customers, ask them to register in the Web site. Unfortunately hackers write programs to make automatic false enrollments which waste the Web site's resources. To solve this problem, systems known as CAPTCHA (completely automated public Turing test to tell computers and humans apart) have been introduced to distinguish between human user and computer program. One of the CAPTCHA methods is collage CAPTCHA. In this method some shapes are shown with distortion and the user is asked to choose a specific object. In this paper we increase the resistance of this method to attacks. For this purpose, we also show some other objects on the right of the screen. Some of these objects are same as the previous objects, but have the different shapes. Now we ask the user to choose a specific object and also its same object on the right of the screen. The user will be passed the test if he chooses the two similar objects correctly. In this method because the computer program should also recognize the similar object, the possibility of passing the test by computer is more reduced.