The Berlin Wall, built in 1961, separated East Berlin, a Soviet sector, from the American, British, and French zones that became known as West Berlin. It stood 12 feet high and stretched for 96 miles. Anyone crossing between East and West Berlin was subject to the scrutiny of armed border guards whose job was to assess whether or not they looked like the photograph they have presented. Guards on the Eastern side of the Berlin Wall had three years of training in a very specific system of facial recognition.
Images: The booklet People's Physical Characteristics, published in 1970 by the Ministry of State Security ("Stasi").
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