1. A copier machine, comprising: a scanner configured to read an image formed on an original sheet; an image forming unit configured to form a copied image on a recording sheet based on image data representing the image read by the scanner; and a control unit configured to control the scanner and the image forming unit and control a copier function of the copier machine to duplicate the original sheet by executing: a first authorization step, in which judgment is made whether predetermined user information was entered, the predetermined user information identifying a user who is authorized to use the copier machine; a reading step, in which, after the first authorization step and when the user is authorized to use the copier machine, the scanner is manipulated to read the image formed on the original sheet; an obtaining step, in which authentication data representing a personal identifying image of the user is obtained from the image data representing the image read by the scanner; and a second authorization step, in which judgment is made whether the authentication data obtained from the image data in the obtaining step indicates permission associated with the predetermined user information for the user to use the copier function, wherein the control unit forms the copied image on the recording sheet when judgment is made that the authentication data indicates permission for the user to use the copier function in the second authorization step, and restricts forming of the copied image when judgment is made that the authentication data does not indicate permission for the user to use the copier function; wherein, when the user identified by the predetermined user information in the first authorization step and the user permitted to use the copier function in the second authorization step are different, the control unit forms the copied image by the copier function permitted to the user permitted in the second authorization step and restricts forming of the copied image by the copier function permitted to the user identified in the first authorization step.