The earliest photography was basically all portraiture. No one wanted photos of THINGS. They wanted photos of themselves, in much the same way that the wealthy kept getting portraits painted. Don't laugh! We have the MySpace shot, afterall, so I'd argue that we're worse.
But by the early 1900's, the increased portability of cameras and film started to foster a sense of artistic possibility, and photos of things, scenes, and places started to emerge. But early on, before the likes of Ansel Adams, photographers thought that their goal should be a movement away from the high-resolution, realistic photos that were being used for portrait shots.
Instead, aspiring artists needed to try to imitate painting with the camera. Photos should appear unrealistic, and instead appear impressionistic. It is in this vein that one of my absolute phavorite photos was taken. It is actually a photo, though it barely appears that way. I generally find myself drawn to this era of photography, I think, because the influence of those like the F/64 Group has been so total, that even if an image is bizarre and unrealistic, it strives for verisimilitude in itself. Focus is always sharp, exposure is always level. Really throwing these rules to the wind and trying to take photos that don't look like photos is thrilling, and especially difficult with modern equipment.