Firstly, what is a VALID representation?
People are multifaceted and the myth of the perfect portrait of someone is probably usually a myth. There are lots of great pictures of people and as others have said snapshots are equally great at capturing unguarded moments even though they are often quite unflattering.
I have photographed a few people who have died before their time and I can tell you that those photographs are some of the most valuable things their love ones own.
In fact a crappy picture from Sears can have more value that a Karsh portrait to someone who loves the subject of the picture.
Also on famous people we tend to put our own spin on what they should look like even though it may just be a caricature of who they really are.
But bottom line is if your life/personality can be captured by a single photograph you are probably a very boring one dimensional individual.
I think the term portrait has really lost all meaning since its overused and in some cases it means vertical.