In an image processing device, the processor performs: (a) setting, as target pixel data, each set of pixel data; (b) selecting, from among the plurality of sets of pixel data, a plurality of first sets of pixel data corresponding to a plurality of first pixels positioned within a prescribed range of the image; (c) determining whether the plurality of first sets of pixel data represents a white background; (d) determining whether a variation in color difference components among the plurality of first sets of pixel data satisfies a prescribed condition; and (e) determining that target pixel data includes mosquito noise when the plurality of first sets of pixel data represents the white background and when the variation in the color difference component among the plurality of first sets of pixel data satisfies the prescribed condition. The prescribed range includes a pixel corresponding to the target pixel data.