Facial recognition requires concepts

Chapter 3 endnote 3, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

...you depend on emotion concepts each time you experience another person as emotional. Knowledge of the concept “Sadness” is required to see a pout as sadness, knowledge of “Fear” to see widened eyes as fearful, and so on.

This phenomenon is not unique to emotion. Even if you simply want to recognize a person in multiple, different photographs, you need a concept for that person.

In one study that demonstrated this phenomenon, test subjects were shown multiple images of two Dutch politicians (faces only, no context) and were asked to sort them into different piles of the same identity. Ideally, the subjects would produce two piles, one per politician, but they did not. Subjects made between 3 and 16 piles, with an average of 7.5 piles. But Dutch subjects who knew these politicians well (that is, who had concepts for the individual politicians) performed almost perfectly.

The moral of the story here is not that Dutch people have an innate circuit for recognizing politicians. Rather, you have a concept for each person whom you know, and you use those concepts to recognize their faces even when the sensory information hitting your retina varies due to the angle of sight, the distance, the light, or other factors. Without those concepts (i.e., when viewing a stranger's face), you have a harder time categorizing different images as depicting the same person.