Forgetting about Photoshop for a minute: you take a picture of someone; that's what they look like. Exactly, in that time, and that place. Captured.
Except that they aren't. A conventional photographic portrait freezes a face in a moment in time. But faces exist in a changing state, as do our perceptions of them. They are never at rest in the way a photograph represents it. Instead of reality, the photo shows an abstraction.
But there's another problem too. We never see a face only in a moment of time; we see faces through layers of history. A photograph isolates a particular collection of features, but in actual vision, these features are always overlaid with the visual memory of all our previous encounters with them (our personal history), and through the layers of our general history with human faces (both real and represented).
From the photograph's point of view, we see everyone as a constant blur of movement, encased by a number of relatively translucent costumes of history. The problem with photography as realism, is that its products are both atemporal and ahistorical, and reality is neither.