An apparatus may include an ultrasonic sensor system and a control system. The control system may be configured to distinguish, according to image data acquired via an ultrasonic sensor system, the pyroelectric effect caused by an actual human finger from the pyroelectric effect caused by a sleeve-type spoof or a “fake finger” spoof. Some such examples involve obtaining multiple frames of ultrasonic image data of a target object on or near a platen of an ultrasonic sensor system via the ultrasonic sensor system and determining at least one target object pyroelectric indication based, at least in part, on the multiple frames of ultrasonic image data.