Postcards were the Instagrams of the early twentieth century. On one day in September 1906, 200,000 postcards were mailed from Coney Island. In 1913 some 968,000,000 postcards were sent in the U.S., more than seven per person. The majority of postcards made at the turn of the twentieth century were mass-produced lithograph or letterpress half-tones, but the Eastern Illustrating & Publishing Company produced "real photo postcards" in the form of silver...