1. A printing device for discharging inks from nozzles according to a set mode and printing an image on a medium, the printing device comprising: a first setting unit configured to set a printing mode of a main image and to set either a front-surface printing mode for printing a background image on the medium and then printing the main image on the background image or a rear-surface printing mode for printing the main image on the medium and then printing the background image on the main image; and a second setting unit configured to set a printing mode of an additional image printed in association with the printing of the main image and to set either a front-surface printing mode for printing a background image for the additional image on the medium and then printing the additional image on the background image for the additional image or a rear-surface printing mode for printing the additional image on the medium and then printing the background image for the additional image on the additional image.