Since an image processing system that can authenticate the originality of digital data adopts an arrangement that does not save and manage digital data in a server, the server scale can be prevented from increasing, and the security can be improved. To this end, in this invention, in an image processing system in which a client and server are connected to be able to communicate with each other, the feature amount and user ID of digital data to be registered are registered in the server, and the digital data is saved in the client in correspondence with the registration number and registration date upon registering the feature amount and user ID.