I Know That Face
Programming Snapshot – Facial Recognition

It is not just Facebook – every Linux user can extract faces from photos and assign them to real people, thanks to free libraries. Mike Schilli shows you how to do it.
Facebook users already take it for granted that the social network recognizes people from their circle of friends by their faces on uploaded pictures. Some free libraries, which every Linux user can download from GitHub, also extract faces from photos and compare them with previously recognized ones, thus allowing the home user to recognize people (e.g., in their private vacation photo collection) and to mark the images accordingly.
Much goes on behind the scenes in automatic face recognition. First, an algorithm has to pick out a face-like object from the millions of pixels in a photo (Figure 1): Two round, slightly darker areas as the eyes; a protruding object in the middle as the nose; a horizontal line below it as the mouth; and another below it as the chin – that could be a face (Figure 2).

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