Postcards first appeared in the 1860's. The first official US postcard was published in 1873. In the 1890's, the growth of tourism, cheaper color lithographic printing and legal rulings made their wide distribution a reality.
By 1907, most postal authorities allowed messages to be written on the back, further increasing their utility. The first twenty years of this century were the golden age of picture postcards.
Postcards were truly an international business. Some of the finest Indian publishers, like Delhi-based H.A. Mirza & Sons and The Archaeological Photographic Works of India, had their postcards manufactured in Germany. The province of Saxony was the world center of quality printing. Postcards were beautifully colorized by the early 1890's, with photo firms typically doubling as postcard publishers. Because postcards often outlive photographs, the dates on them can offer important clues to a photographer or firm's fate and works.
Postcard collecting remains a popular subculture. In America, most towns have clubs and annual fairs. There are plenty of old South Asian views available. Occasionally, handwritten Hindi postcards turn up, like ones sent from Bombay to Jaipur ninety years ago, only to finally arrive in the hands of a Midwestern hobbyist.
Above: Exterior of Zenana, Agra. Tuck's Oilette, London, ~ 1915.