Secure CAPTCHAs via Object Segment Collages

CAPTCHA, a short form of “Completely Automated Public Turing test to Tell Computers and Humans Apart”, is a computer program that can generate and grade tests that most humans can pass, but current computer programs cannot. This paper advances research on image-based CAPTCHA by incorporating the object segment collages. We first collect object segments from thousands of images by using our self-developed collection tool. Then, we create an image collage that compiles randomly selected object segments. To increase the difficulty for computer detection algorithms, we embed some features such as noisy background, object segment occlusion and object segment orientation update. We also develop a practical application using the newly proposed Object Segment Collage CAPTCHA. For the evaluation, we measure the accuracy performance of computer vs. human in solving CAPTCHA questions. In addition, we also conduct a user study over different CAPTCHA methods.