1. A resolution determination device, comprising: an edge strength calculator configured to obtain an edge strength of a pixel included in an input image based on luminance of the pixel and luminance of a pixel adjacent to the pixel, for each of a plurality of pixels included in the input image; and a resolution determiner configured to determine whether or not the input image is an image upconverted from an image with a predetermined resolution or less, based on distribution of the edge strengths, and output a determination result.