1. An image processing device comprising: a memory configured to store a plurality of captured images; and a processor comprising hardware, wherein the processor is configured to implement: an image selection unit configured to: select a reference image from among the plurality of captured images stored in the memory; and select candidate images to be combined with the reference image from a first group of images and a second group of images among the plurality of captured images, if the reference image is neither the earliest captured image nor the latest captured image stored in the memory, wherein the first group of images being captured earlier than the reference image; and the second group of images being captured later than the reference image; and a composition processing unit configured to compose the candidate images to be combined selected by the image selection unit with the reference image selected by the image selection unit to generate a composite image.