1. A method of detecting liveness, comprising: obtaining a single ultrasonic image of a biometric object; subdividing the single ultrasonic image into a plurality of overlapping sample blocks; extracting feature vectors in a spatial domain and a frequency domain from each of the plurality of sample blocks, the feature vectors including a histogram feature, the histogram feature including ultrasonic impedance characteristics of ridges and valleys of the biometric object; and comparing the feature vectors from each of the plurality of sample blocks to a classification model.