Method for providing a completely automated public Turing test to tell computers and humans apart, CAPTCHA, comprising the steps: (la) sending, by a browser or web application of a client, a request for providing a CAPTCHA to a server; generating, on a server, a set of pictures, the set containing at least two pictures, wherein each of the pictures is assigned a unique identifier, and a temporal identifier which is generated by each request based on the unique identifier; and sending the set of pictures and the temporal identifiers, and the assignment between temporal identifiers and pictures to the browser or web application; generating, on the server, a question that is associated with one or more of the pictures of said set, and wherein the question is assigned a question identifier; sending the question and the question identifier to the browser or web application; and storing, on the server, the temporal identifiers assigned to the pictures, with which the question is associated, and the question identifier; (1b") distributing the pictures of the set to one or more subset(s) of pictures, wherein each of the subsets comprises at least two pictures; (1b"') defining, for each of the subsets, a presentation position within the browser or web application, and generating, for each of the subsets, an enumeration for the pictures of the respective subset; presenting, in the browser or web application, the question; presenting, consecutively, in the browser or web application, for each of the subsets at the position defined in step (1b'") any of its pictures for a predetermined presentation time, wherein the pictures of the respective subset are presented in the order of the enumeration of the pictures in that subset, wherein, for each of the pictures or subsets presented, the browser or web application detects whether or not the user performs a confirmation action during the presentation time of the picture, and wherein, when the browser or web application has detected a confirmation action, the temporal identifier(s) assigned to the presented picture(s) while the confirmation action has been performed and the question identifier are sent to the server; if one or more temporal identifier(s) and the question identifier have been received by the server from the client: checking, by the server, for identity of the temporal identifier(s) sent to the server in the foregoing step and the temporal identifier(s) stored in step for the question identifier received in this step; if identity has been confirmed in the foregoing step: sending, by the server, information that the CAPTCHA has been successfully passed to the to the client; otherwise: sending, by the server, information that the CAPTCHA has not been successfully passed to the client. (la) sending, by a browser or web application of a client, a request for providing a CAPTCHA to a server; generating, on a server, a set of pictures, the set containing at least two pictures, wherein each of the pictures is assigned a unique identifier, and a temporal identifier which is generated by each request based on the unique identifier; and sending the set of pictures and the temporal identifiers, and the assignment between temporal identifiers and pictures to the browser or web application; generating, on the server, a question that is associated with one or more of the pictures of said set, and wherein the question is assigned a question identifier; sending the question and the question identifier to the browser or web application; and storing, on the server, the temporal identifiers assigned to the pictures, with which the question is associated, and the question identifier; (1b") distributing the pictures of the set to one or more subset(s) of pictures, wherein each of the subsets comprises at least two pictures; (1b"') defining, for each of the subsets, a presentation position within the browser or web application, and generating, for each of the subsets, an enumeration for the pictures of the respective subset; presenting, in the browser or web application, the question; presenting, consecutively, in the browser or web application, for each of the subsets at the position defined in step (1b'") any of its pictures for a predetermined presentation time, wherein the pictures of the respective subset are presented in the order of the enumeration of the pictures in that subset, wherein, for each of the pictures or subsets presented, the browser or web application detects whether or not the user performs a confirmation action during the presentation time of the picture, and wherein, when the browser or web application has detected a confirmation action, the temporal identifier(s) assigned to the presented picture(s) while the confirmation action has been performed and the question identifier are sent to the server; if one or more temporal identifier(s) and the question identifier have been received by the server from the client: checking, by the server, for identity of the temporal identifier(s) sent to the server in the foregoing step and the temporal identifier(s) stored in step for the question identifier received in this step; if identity has been confirmed in the foregoing step: sending, by the server, information that the CAPTCHA has been successfully passed to the to the client; otherwise: sending, by the server, information that the CAPTCHA has not been successfully passed to the client.