1. A method for constructing a unified biometric image, the method comprising: receiving a sequence of images of biometric data from a biometric recognition sensor; as the images of biometric data in the sequence are received, repeatedly selecting a sliding window of images of biometric data from the sequence, wherein: each sliding window comprises a subset of the images of biometric data in the sequence, and a number of images of biometric data in each subset comprises: at least two of the images of biometric data in the sequence but less than a total number of the images of biometric data in the sequence, and at least one image of biometric data that is not included in a preceding sliding window; selecting one or more images of biometric data from the subset of images of biometric data in at least one sliding window; and including the selected one or more images of biometric data in the unified biometric image.