disclosed is a method of providing a completely automated public turing test to tell a computer and a human apart based on image . the method comprises the steps of : storing a plurality of randomly - selected images by session when a request for a web page is received from a user client ; providing the web page and a session id to the user client ; generating a test image by mixing the plurality of images when a request for a test image corresponding to the session id is received from the user client ; transmitting the generated test image to the user client ; receiving at least one of first identification information inputted by the user about the test image from the user client ; and comparing the first identification information with second identification information included in meta information of the test image .