There is provided an image processing apparatus which comprises: a receiving unit configured to receive a print job from an information processing apparatus; an obtaining unit configured to obtain at least owner information and domain information from a header of the print job; a generating unit configured to generate user identification information including the owner information and the domain information; a registering unit configured to register the user identification information; and a storage unit configured to store the print job in association with the user identification information. Thus, it is possible to register the appropriate user identification information according to environments of a network system.