Ultrasonic antispoof using multiple acoustic channels

A computing device, comprising:

• a display device that is provided by a front side of the computing device;
• a speaker that is provided by the front side of the computing device;
• a first microphone that is provided by the front side of the computing device;
• a second microphone that is provided by a rear side of the computing device that is opposite the front side of the computing device;
• one or more processors;
• and
• one or more computer-readable devices including instructions that, when executed by the one or more processors, cause the computing device to perform operations that comprise:
• outputting, by the speaker, an acoustic waveform;
• recording, by the first microphone, a first reflection of the acoustic waveform that was output by the speaker;
• recording, by the second microphone, a second reflection of the acoustic waveform that was output by the speaker;
• determining a computed representation of an environment surrounding the computing device, based on the first reflection of the acoustic waveform and the second reflection of the acoustic waveform;
• providing the computed representation of the environment surrounding the computing device to a computational model that is configured to determine whether the computed representation of the environment surrounding the computing device indicates presence of a human face;
• and
• receiving, from the computational model, an indication that the environment surrounding the computing device includes a human face.