1. An imaging device comprising: a far-infrared camera configured to capture an image of a scene using a far infrared ray in a first wavelength band and generate a far-infrared camera image; a near-infrared camera configured to capture an image of the scene using a near infrared ray in a second wavelength band shorter than the first wavelength band and generate a near-infrared camera image; a low-level region detection unit configured to detect a low-level region with a predetermined level or less from the far-infrared camera image; a transparent region detection unit configured to detect a low-level region as a transparent region based on at least the near-infrared camera image, the low-level region having the predetermined level or less resulting from being a transparent region that is a region covered with a visually transparent material, within the low-level region detected by the low-level region detection unit; an image segmentation unit configured to segment a portion of the transparent region from the near-infrared camera image; and a superimposition unit configured to superimpose the portion of the transparent region onto a position of the far-infrared camera image, the position corresponding to a position of the transparent region, and generate a synthetic image.