Self Portrait

What makes an effective portrait? Whether a pencil sketch, an oil painting, a written biography or a photograph, the impression such a representation makes is always clouded by the viewer's internal interpretation. When the medium is photography (leaving aside the question of digital manipulation), there is an added dimension- that of an assumed reality (one less step of abstraction.) When the subject creates his or her own self-image, ie.; the viewer and the subject are the same person, is the validity of the image enhanced, diminished or otherwise altered?
When the subject looks directly at the camera, with a mirror or the led screen reflecting the face, especially the eyes, what meaning is imparted? The person one wants to be? The real person beneath the pose? A little of both? And what can other viewers make of this image? How many layers of preconceptions, life experiences, gender and age considerations, previous knowledge of the subject, epectations and aspirations of this mysterious "Other" are there? Who are you? Who am I?