http://cvcl.mit.edu/papers/IsolaXiaoTor ... PR2011.pdf
Very interesting paper describing how to measure and predict a photo's memorability. Not surprisingly, photos of people are very memorable. Landscapes are least memorable, mountains especially. Though I bet this audience would skew that statistic a bit. Semantics matter to memorability. To most people a portrait is not just a portrait, it's "an attractive male, about twenty-five, with dark hair and blue eyes", but they probably don't distinguish beyond "a photo of a mountain", whereas to some of us it's "a class 4 ridge, looks like granite, over a highly crevassed glacier in an alpine/arctic valley, probably northern Rockies or Alaska".