To make any more sense of the appropriative nature of photography, we have to get a couple of things clearly understood in our own minds. There are objects in the world, with a reality of their own, they are physical things which exist. Tables, chairs, buildings, people, trees, and so on. Corresponding to these real objects, there are ideas of those objects which we have in our minds, and relationships we have to those objects. How I feel about that table, how society as a whole feels about Angelina Jolie, my Idea of my wife.
The second kind of thing is abstract, vague, intangible. It's also more important than the first thing. There are deep questions of philosophy and quantum physics which I don't care about and which don't matter here: Whether and how a tree "exists" without the presence of an observer, and how that observer changes and alters its reality I neither know nor particularly care. We can say with confidence that an unobserved tree is not very interesting to anyone, and that's all that matters. The point here is that our personal and societal ideas about objects are what's important, ultimately, precisely because an unobserved object is -- at best -- pretty uninteresting.
You would argue that a giant meteor, as yet unobserved, but aimed to obliterate the Earth is pretty interesting, but I maintain that it's not interesting until we, however briefly, observe its existence.
Let's also take a moment to discard the notion that an image partakes in some literal way in the reality of the thing imaged. Whether true or not, I am not interested here in notions of voodoo, or the idea that a photograph steals ones soul. These are idea that go back a long ways, but in modern society we tend not to believe them (at least not to admit it), and anyways what I am trying to get at is what might underlie such a belief.
A photograph alters, however minutely, our idea of the object photographed. An image might not literally diminish other elements of our idea of the object, but by creating new aspects of that idea it makes the other aspects relatively smaller. Our experience of an actual McDonald's hamburger is a real thing in our mind. Images of that hamburger add to that idea, that mental model of the McDonald's hamburger. While our real experience is not diminished, advertisers can alter our overall attitude by filling our mind with competing images of delicious and desirable hamburgers. The image of the burger grows with each photograph and video, the actual experience diminishes in importance. This is why advertising works.
In this same way our society's understanding of Winston Churchill is largely driven by a single iconic image, the cigar-less portrait made by Karsh. Our relationship with Half-Dome, whether we have seen it or not, is largely defined by Adams photographs and the infinite cloud of copies made by everyone. The Eiffel tower has no particular iconic photograph that I know of, but has certainly been reduced to a postcard in our minds, and is well on its way to becoming a snapshot containing a blurry black object behind a pair of vapidly grinning tourists. Celebrities are featherless bipeds who exist primarily in photographs and videos.
Consider a homeless man named Bill. Bill has, perhaps, a little trouble with beer. Maybe Bill's wife died in a car accident 20 years ago, perhaps Bill knows the lyrics to every Journey song. This is Bill to the dozen or so people who actually know Bill. Now some idiot with a fedora and a Canon 5DII comes along doing some "street photography" and takes a picture of Bill. This picture is over-processed and dumped on to flickr. At this point Bill's actual reality is unchanged. The idea of Bill in the minds of his dozen-ish friends is also unchanged. The idea of Bill has, however, been introduced to a couple hundred hipster idiots, who now know Bill as the freaky looking homeless dude in that one picture. Has Bill been hurt or diminished at this point? It's not clear to me.
Multiply this by 5 or 6 other hipsters with cameras. Let's suppose Bill's particularly interesting looking, or locally famous for his Journey renditions. A picture of Bill gets into the newspaper, or onto the news. Now Bill's friends, the dozen or so people, have an element of Bill as the-guy-in-that-photo introduced into their minds. Bill has been diminished in a meaningful way at this point. People he knows have a new perception of Bill, and part of that is based on a picture, not on Bill. Bill is smaller. Perhaps Bill prefers being the guy in the picture. Many celebrities, large and small, seem to prefer the image of themselves to the real thing, or at any rate seek to enlarge that shadow reality, that false copy of themselves.
The shadow world of photographs, as I have noted repeatedly, is growing and changing at a furious pace, and I wonder a lot what it all means.