1. An image generation device comprising: a processor; and a memory device that stores a plurality of instructions, wherein when the processor executes the instructions in the memory device, the processor is operable to: acquire an image to be processed; acquire region information specifying a region to be processed in the image; acquire a feature parameter indicating a feature of the region specified by the region information acquired and affecting a motion of liquid; acquire an image to be superimposed based on image-to-be-superimposed information stored in association with the acquired feature parameter of the region by referring to a storage storing in association with each other a feature parameter affecting a motion of the liquid and the image-to-be-superimposed information for acquiring an image to be superimposed where the liquid in motion is shown; superimpose the image to be superimposed on the region; and output the image to be processed.