To keep it simple, what we actually want to achieve, is to identify a person given an image of his / her face, e.g. the input image. The way we do that, is to provide one (or more) image(s) for each person we want to recognize, labeled with the persons name, e.g. the reference data. Now we compare the input image to the reference data and find the most similar reference image. If both images are similar enough we output the person’s name, otherwise we output ‘unknown’.