Disclosed is a method of providing a completely automated public turing test to tell a computer and a human apart (CAPTCHA) 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.