1. An image processing device comprising: a processor; and a memory storing computer-readable instructions therein, the computer-readable instructions, when executed by the processor, causing the image processing device to perform: setting a focal pixel among a plurality of pixels in an original image that is represented by original image data; setting a pixel near the focal pixel as a near pixel; acquiring a degree of difference in luminance for the focal pixel and the near pixel; determining, based on the degree of difference, at least one of: a size of a supplemental image; a shape of the supplemental image; color of the supplemental image; and luminance of the supplemental image; and generating edited image data by editing the original image data, the edited image data representing an edited image obtained by superimposing the supplemental image on the original image, the supplemental image being superimposed on an area around the focal pixel in the original image.