If you happen to live in a big city, you probably have noticed huge advertisements on the sides of buildings. Not digital billboards or vinyl sheets with computer-printed graphics. But hand-painted art, literally as big as a building.

“Walldogs” is the industry term for the people who paint these murals. It is also the name of a Los Angeles-based company that does that kind of work here in town.

Owner Riley Forsythe has been in the business of painting advertisements and billboards for 40 years. Outdoor advertising and billboards were much more difficult to create in the pre-digital era.

“Before 1990, all the large billboards, including Los Angeles, were all hand-painted. Most people don’t know that,” says Forsythe. “All of us were trained to paint photo-realistically, to reproduce the artwork as accurate as possible on these billboards, at scale.”

Listen to the full interview with Forsythe in the audio player above.