When a selection for canceling a security image is input at a client computer, then a password authentication unit causes a display unit to display a password reception screen, whereby an input password is compared with an authentication password stored in a password storage unit. When the passwords are matching, the print data generation unit of the client computer generates print data without adding a security image to the original data, and outputs the print data to a print server. A control unit of the print server transfers the print data to a printer, a print log acquisition unit acquires print log information from the printer, and the print log information and print data are stored in a print information storage unit.