Wim Wenders has a photograph on his desk that moves him to tears every day. It’s by Sebastião Salgado, the Brazilian aesthete-adventurer who was once an economist before deciding to explore the material welfare of humankind more personally, in pictures. Results of that decision make up the substance of Wenders’ spellbinding new documentary, a deep survey of Salgado’s career, co-directed with the photographer’s son Juliano. Given the grace and emotional intelligence with which Wenders habitually imbues his own works of portraiture (see also Pina and The Buena Vista Social Club), it’s no stretch to say Salgado seems like a kindred spirit. The Salt of the Earth necessarily contains many harrowing images of human suffering — indeed, famine and war are Salgado specialties — but the effort to make and collect these images registers here as the opposite of exploitation. Wenders’ presentation is un-fussy and direct, a model of eloquently conversational narration and judiciously selected images. It’s also a valuable and affecting endorsement: Through his life’s work, Salgado has earned the authority to advocate for a less destructive, more cherishing engagement with nature, which includes trees and animals and, especially, human beings.