Online Collage CAPTCHA
In some websites it is necessary to tell apart human users from computer programs which is known as CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart). CAPTCHA methods are mainly based on the weak points of OCR 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 objects are chosen randomly and the pictures about these topics are downloaded from Internet. Then after effecting some changes such as rotating, all of the pictures 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 and not a computer software. The main advantage of this method is its simplicity because the user does not have to type anything.