“No matter how artful the photographer, no matter how carefully posed his subject, the beholder feels an irresistable urge to search such a picture for the tiny spark of contingency, of the here and now, with which reality has (so to speak) seared the subject, to find the inconspicuous spot where in the immediacy of that long-forgotten moment the future nests so eloquently we, looking back, may rediscover it. ” -Walter Benjamin, “A Little History of Photography”
(Possibly, this may also explain the allure of the disposable camera in the era of Instagram.)
puellaludens.com 
Now days, what would Benjamin think of the instant and endless memory of photography?