Collage CAPTCHA
Nowadays, many daily human activities such as education, commerce, talks, etc. are carried out through the Internet. In cases such as the registering in websites, some hackers write programs to make automatic false enrolments which waste the resources of the website while this may even stop the entire website from working. Therefore, it is necessary to tell apart human users from computer programs which is known as CAPTCHA (completely automated p[ublic turing test to tell computers and human apart). CAPTCHA methods are mainly based on the weak points of OCR (optical character recognition) systems while using them are undesirable to human users. In this paper a method has been presented for telling the human users and computer softwares apart on the basis of choice of an object shown on the screen. In this method some pictures are chosen randomly and after effecting some changes such as rotating, all of them are shown on the screen. Then we ask the user to choose a specific object. If the user chooses the right object we can guess that the user has been a human being not computer software. The main advantage of this method is its simplicity because the user does not have to type anything. This method has been implemented by the Java programming language.