The present disclosure provides an image generating device that includes processing circuitry configured to acquire positional information indicative of a position of a water-surface movable body where an imaging device is to be installed, acquire posture information indicative of a posture of the water-surface movable body, acquire additional display information including information indicative of positions of a plurality of locations, generate three-dimensional display data for displaying a graphic indicative of the additional display information by superimposedly placing the graphic on a water surface portion of an image outputted from the imaging device based on the positional information, the posture information, and the positions of the plurality of locations included in the additional display information, and output the graphic rendering the three-dimensional display data.