A scanning device includes a visible light source, an infrared light source, a visible light sensor and an infrared light sensor. The visible light source provides visible light to a scan section of an original. The original reflects the visible light to generate reflected light. The infrared light source provides infrared light to the scan section. The infrared light penetrates through the original to generate penetrating light. The visible light sensor receives the reflected light at a first scan position and generates a visible light image signal representative of a visible light image of the scan section. The infrared light sensor receives the penetrating light at a second scan position and generates an infrared light image signal representative of an infrared light image of the scan section. A relative positional relationship between the first and second scan positions is fixed.