A method includes capturing a first image of an object at a first time using a camera and assigning shade values to a plurality of pixels in a portion of the first image. The object includes a light portion and a dark portion that is darker than the light portion. The method further includes identifying a first mode value of the shade values corresponding to the light portion of the object in the first image, and identifying a second mode value of the shade values corresponding to the dark portion of the object in the first image. The method further includes determining a difference between the first and second mode values, and determining a contrast of the first image based on the difference.