text: (CNN)As art, film stills are often overlooked. 
  
  The photographers tend to be anonymous; it's easy to imagine their work done by the director or cinematographer. Their images are often lumped in with the promotional machinery: Whether documenting the stars frolicking on set or getting down to business, it's just another form of salesmanship. 
  
  Which is why the work of Ernst Haas is so striking. 
  
  Haas, one of the 20th century's great photojournalists and image-makers -- an early member of the great Magnum Photos cooperative who was famous enough in his prime to have been the subject of a Museum of Modern Art exhibit in 1962 -- was also a regular on movie sets. It was a necessity in those early days, said John Jacob, the editor of a new book of Haas' movie photography, "Ernst Haas: On Set." 
  
  "Working on film sets was really important to Magnum, and all of the photographers working with Magnum in the '50s did films," says Jacob, now the McEvoy Family Curator for Photography at the Smithsonian American Art Museum. Not only did the work pay off financially, but the photographers also established relationships with members of the industry, he said. 
  
  And the stars and directors knew what they were getting: some of the best in the field. Photographers such as Haas were entrusted to bring their talent and style to the work. 
  
  The photographers "are definitely producing work for posterity, that very much has their own fingerprint on it," Jacob said. 
  
  Such distinction is obvious from looking at Haas' work -- some of which is as famous as the movies he worked on. 