Perceptual Constancy
Perceptual Constancy is also referred to as Object Constancy or Constancy Phenomenon. Perceptual Constancy refers to the inclination to identify and interpret well-known objects as having a constant shape, size, color, location and brightness despite changes in the distance, angle of viewpoint and lighting.
This is what enables the person to recognize a familiar face regardless of the fact that the face is covert.