1. An image processing device, comprising: a display control unit that generates a composite image that is a surrounding image of a vehicle viewed from a virtual viewpoint, based on an input image input from each of a plurality of in-vehicle cameras, and that causes a display unit to display the composite image; a pattern specification unit that specifies an image pattern to be output as the input image among a plurality of image patterns for each of the in-vehicle cameras; and a pattern collating unit that determines whether all of a plurality of image pattern responses transmitted from the in-vehicle cameras match with the image pattern; wherein the display control unit causes the display unit to display a certain preparation image when a display switching condition to the composite image is satisfied, and causes the display unit to display the composite image instead of the preparation image, when the pattern collating unit determines that all of the image pattern responses match with the image pattern.