It may be hard to imagine now, but picture postcards used to play a huge role in American life. Postcards were mailed and collected by the hundreds of millions every year. Across the U.S., images of Chicago and Illinois were particularly popular. A book called Picturing Illinois takes a closer look at these iconic 20th century postcards. We revisit a conversation with the book's authors: John Jakle, professor emeritus at the University of Illinois at Urbana-Champaign and Keith Sculle, former head of research and education at the Illinois Historic Preservation Agency. View a slideshow of 20th century postcard art.