One thing is certain: There is not, and will not be, an ecology of images. (Sontag acknowledged as much in her last book, “Regarding the Pain of Others,” published in 2002). Images make up our ecosystem, our native habitat, the only reality we recognize. And as we learn to negotiate the landscape of digital culture, the history of photography can provide a compass and a map. The camera, the darkroom, the museum and the archive all exist in the same place. Everywhere and nowhere; on Google Earth, in social networks, on a standard cellphone app. Every one of us commands a factory and a storehouse of images, vessels of information and nostalgia, desire and curiosity. And each of us spends more time than we care to admit browsing through it, searching out shards of memory and intimations of mortality.