Face Perception

"There is an universal tendency among mankind to conceive all beings like themselves, and to transfer to every object, those qualities, with which they are familiarly acquainted, and of which they are intimately conscious. We find human faces in the moon, armies in the clouds; and by a natural propensity, if not corrected by experience and reflection, ascribe malice or good- will to every thing, that hurts or pleases us."
— David Hume, The Natural History of Religion.

Seeing faces in inanimate objects is a form of Pareidolia, this is a psychological phenomenon involving stimulus, usually from a image or sound, that is perceived to be significant.
In contrast, there is a condition called 'face blindness' or Prosopagnosia, where the ability to recognise faces in normal everyday life, your family or friends for example, is impaired.
People with Prosopagnosia may find it difficult to socialise and so other cues such as voice, clothing and body shaped can be used to aid them. Read this account, where a women with the condition explains further and how she recognises faces in relation to stones.