Image processing device and image processing method

The present invention aims to provide an image processing device and an image processing method whereby a composite image and an expanded image can be readily obtained, when a building structure comprising a plurality of planes is captured using split-photography. This image processing device comprises: an image acquisition unit that obtains a plurality of captured images having each of the different sections of the building structure comprising the plurality of planes captured therein; a plane specification unit that specifies a common plane shared by the plurality of captured images; an image conversion unit that performs projective transformation of images having a common plane, among the plurality of captured images, and generates a plurality of converted images having the common plane facing; a composite image generation unit that generates a planar composite image having a plurality of converted images synthesized in the same plane; and an expanded image generation unit that joins a plurality of planar composite images and generates an expanded image of the building structure.