Although postcards were traditionally used as a means for travel correspondence, they have broadened their function since being introduced in the 19th century to include marketing, advertising and other business-related purposes.
Postcards first became popular in Austria in 1869 and, over the next few decades, were introduced to the United States. In 1906, Americans were buying an average of 700 million postcards a year, according to Columbia Daily Tribune.
"Postcards served many purposes when they were at the peak of popularity," writes Nancy Russell for the Tribune. "They were a way to communicate as well as a way to remember where you had been on your travels. They were colorful and inexpensive to buy and to mail. A penny stamp was all it took to have informal communication with family and friends."
Sales of postcards stumbled after reaching their peak of 968 million cards in 1913. However, the 1960s saw a resurgence of the old hobby, as collectors began to see the item as a window into the past.
Postcards are still popular collector's items, but they are also widely used as marketing materials and correspondence tools.