1. An image sensor, comprising: a plurality of photosensitive sites arranged into an active area and a non-active area, wherein the photosensitive sites in the active area are used to capture an image; and a metal plate covering at least a portion of the photosensitive sites in the non-active area, wherein the metal plate includes one or more openings positioned at predetermined locations over respective photosensitive sites in the non-active area to form a unique pattern that is associated with the image sensor.