Swiss-born American photographer Robert Frank won the top prize at Spain's international photography festival Monday.Frank, regarded as one of the 20th century's most important photographers, will receive a trophy and a prize of 12,000 euros (US$16,000) at the PhotoEspana event."His works on life in the U.S., published in the book 'The Americans,' marked a way of seeing and looking that has profoundly influenced later generations," PhotoEspana organizers said in a statement."His beat aesthetics and his film and photography projects have helped to make photography be considered as a major art," it added.Frank began a road-trip across the United States in 1954 and published a book of photos taken during the trip called "The Americans" four years later which is considered to be his most notable work.Born in Zurich, Switzerland in 1924, he emigrated to the United States in 1947 where he worked for magazines including McCall's, Vogue, and Fortune.Past recipients of PhotoEspana's top prize include Japan's Hiroshi Sugimoto, the Czech Republic's Josef Koudelka and Nan Goldin of the United States.PhotoEspana, one of the largest photography festivals of its kind, began on May 30 and runs till July 22 in Madrid. It has been held each year since 1997.Exhibits at this year's festival include political portraits by Frenchman Raymond Depardon, portraits of Africa by Brazilian Salgado and pictures taken by celebrities such as actor Richard Gere and musician Lou Reed.