Prosopagnosia is a special form of visual agnosia. The condition involves an inability to recognize faces, even in the case of close family members and even oneself in the mirror! But the inability applies only to the face. If the "unknown" begins to speak, or moves in a somewhat characteristic way, or wears a familiar piece of clothing, he is immediately "exposed". The condition is most pronounced if the damage is in the right hemisphere of the brain and especially in the gyrus fusiformis.
It has long been well known that the right hemisphere of the brain is specially equipped with the ability to analyse patterns and shapes of various kinds, especially in the left half of the visual field. Remember that the left hemisphere of vision is analyzed in the right hemisphere of the brain! This is probably reflected in the fact that injuries in the neck-crown area of the right hemisphere, such as neglect, cause more severe and prolonged functional impairments than those affecting the left hemisphere, with the exception of disorders involving language functions, of course.