1. A printing apparatus for printing an image on a medium, comprising: a first head unit; a second head unit that is located upstream from a transport direction from the first head unit; a controller that performs printing control that prints a first image, a second image which is different from the first image, and a background image, based on a separately selectable mode without moving the first head unit and the second head unit; wherein, when a first mode is selected, the controller performs printing control that prints the first image to the medium, prints the background image to the first image using the second head unit, and prints the second image to the background image using the first head unit, and when a second mode is selected, the controller performs printing control that prints the second image to the medium, prints the background image to the second image using the second head unit, and prints the first image to the background image using the first head unit.