1. A method of surveilling a subject including a person's body comprising: interrogating the subject with electromagnetic radiation in a frequency range of about 100 MHz to about 2 THz; generating, from the interrogating, image data representative of at least a first image of at least a portion of the person's body; identifying from the image data at least a first portion of the body; and determining from the image data at least a first feature of the image based at least partially on the identified portion of the body.