Museum directors and curators on what they look for in a photograph

Britt Salvesen of Los Angeles County Museum of Art outlines why self-portraiture unites the collection, Urs Stahel, formerly of the Fotomuseum Winterthur, explains the significance of Hans-Peter Feldmann's approach, while images "need to have musclepower, mean something and please the eye", says Els Barents of Huis Marseille. (06:00) Paris, 2012