Patent ID: 8352598

Claim:
A method of providing an image-based completely automated public turing test to tell computer and humans apart (CAPTCHA), the method comprising 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 together as one image 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 first identification information inputted by the user client about the test image; and comparing the first identification information with second identification information included in Meta information of the test image, wherein the session ID is provided along with the session start time information, hash values of the second identification information produced by a hash function, salt information for producing the hash values of the second identification, and signature value generated by signing the session start time information, the hash values of the second identification information, and the salt information using a secret key in the step of providing the web page.