An accomplished photographer who lets the public use thousands of her images of America for free has sued the Getty Images photo agency for more than $1 billion, saying it’s improperly selling her work to customers and threatening those who don’t pay. Carol Highsmith, whose work has been featured in books, newspapers and magazines and on two postage stamps, said she became aware that Getty was selling her work in December, when she received a letter from an affiliated company accusing her of copyright infringement for using one of her own photographs on the website of her nonprofit This is America Foundation. The photo, of a striking sculpture of a badminton shuttlecock outside the Nelson-Atkins Museum of Art in Kansas City, Mo., was one of thousands Highsmith has made available to the public through the U.S.