1. An image processing device, the image processing device comprising a processor configured to: specify as an image pattern for each of a plurality of in-vehicle cameras, an image area that is obtained by selecting a certain area from anions image areas of an image captured by the corresponding in-vehicle camera and is to be output as an input image of the corresponding in-vehicle camera; in response to the image pattern being specified, receive the image areas respectively transmitted from the plurality of in-vehicle cameras along with respective image pattern responses; generate a composite image that is a surrounding image of a vehicle viewed from a virtual viewpoint, based on the image areas received from the plurality of in-vehicle cameras; determine whether all of the image pattern responses transmitted from the in-vehicle cameras match with the specified image pattern; and display a certain preparation image when a display switching condition to the composite image is satisfied, and display the composite image instead of the preparation image, when it is determined that all of the image pattern responses match with the specified image pattern.