1. A sensing apparatus comprising: an input unit configured to input an image; a face detection unit configured to detect a face of a person from the image input from said input unit; a first calculation unit configured to calculate a pupil-feature amount associated with an eye open/closed state from faces detected from a plurality of images input from said input unit within a predetermined time; a second calculation unit configured to calculate, as a feature-change amount, a difference between the pupil-feature amount calculated by said first calculation unit and a feature amount calculated from a face detected from an image input before a predetermined time; a weighting unit configured to determine weights for the pupil-feature amount calculated by said first calculation unit and to determine weights for the feature-change amount calculated by said second calculation unit, wherein the weights are determined on the basis of a plurality of pupil-feature amounts calculated by said first calculation unit from the plurality of images, and wherein the weighting unit is further configured to set the determined weights for the pupil-feature amount and for the feature-change amount; a determination unit configured to determine whether the eyes of the face detected by said face detection unit are open or closed on the basis of the pupil-feature amount and the feature-change amount for which said weighting unit sets the weights; and a recording unit configured to record the input image if the eyes are determined to be open, wherein said weighting unit sets the weight for the feature-change amount to be larger than the weight set for the pupil-feature amount when a difference between a maximum value and a minimum value in a plurality of pupil-feature amounts calculated by said first calculation unit from the plurality of images is smaller than a predetermined threshold.