A sensing mechanism for an image-forming device of one embodiment of the invention is disclosed that includes a first light source, a second light source, a detector, and a controller. The first light source is positioned incident to a first side of media, whereas the second light source is positioned incident to a second side of media opposite of the first side of the media. The detector is positioned incident to the second side of the media to detect first light transmitted through the media as output by the first light source, and to detect second light reflected off the media as output by the second light source. The controller is to detect at least one characteristic of the media based on a ratio of the first light to the second light.