A computer is provided with an application and a printer driver. A user of the computer generates image data using the application. When the image data is for a plurality of pages, the user selects a desired watermark for each of the plurality of pages. The printer driver converts the image data into print data, and combines selected watermarks with the print data for corresponding pages, thereby generating updated print data. The updated print data is output as a single print job to the printer. The printer executes printing operations based on the print job so as to an image on a plurality of pages each formed with a corresponding watermark.