1. An image processing device comprising: a standard image input device for inputting a standard image obtained by imaging; a reference image input device for inputting a reference image obtained by imaging at a viewing angle different from a viewing angle when capturing the standard image; a specific shape candidate detection device for estimating and detecting a shape surrounded by straight lines from the standard image input from the standard image input device as a specific shape candidate having a specified shape; a virtual target object information generation device for generating virtual target object information for specifying a virtual target object image obtained in a case of imaging a target object represented by the specific shape candidate detected by the specific shape candidate detection device at a viewing angle different from the viewing angle when capturing the standard image; a virtual target object image detection device for detecting the virtual target object image from the reference image input from the reference image input device using the virtual target object information generated by the virtual target object information generation device; a shape determination device for determining the specific shape candidate detected by the specific shape candidate detection device as a specific shape having the specified shape when the virtual target object image has been detected by the virtual target object image detection device; a generation control device for controlling the virtual target object information generation device so as to generate the virtual target object information for specifying the virtual target object image obtained by changing at least one of the size and the position of the virtual target object image when the virtual target object image has not been detected by the virtual target object image detection device; and a repetition control device for repeating detection processing in the virtual target object image detection device, determination processing in the shape determination device, and control processing in the generation control device.