In his influential essay "Little History of Photography," originally published in 1931, Walter Benjamin quotes Bertold Brecht on photography:

Less than ever does the mere reflection of reality reveal anything about reality. A photograph of the Krupp works or the AEG the massive German armaments and electric companies, respectively--- tells us next to nothing about these institutions.

...on one level, there is no doubt that Brecht was right. Photographs don't explain the way the world works; they don't offer reasons or causes; they don't tell us stories with a coherent, or even discernible, beginning, middle, and end. Photographs live on the surface: they can't burrow within to reveal the inner dynamics of historic events. And though it's true that photographs document the specific, they tend, also, to blur---dangerously blur---political and historic distinctions: a photograph of a bombed-out apartment building in Berlin, circa 1945, looks much like a photograph of a bombed-out apartment building in Hanoi, circa 1969, which looks awfully similar to a photograph of a bombed-out apartment building in Baghdad from last week.

Linfield says that:

what photographs succeed in doing, which is to offer an immediate, emotional connection to the world. People don't look at photographs to understand the inner contradictions of monopoly capitalism or the reasons for the genocide in Rwanda. They---we---turn to photographs for other things: for a glimpse of what cruelty, or strangeness, or beauty, or suffering, or love, or disease, or natural wonder, or artistic creation, or depraved violence, looks like. And we turn to photographs, also, to find out what our intuitive reactions to such otherness might be.