3D is improving all the time. Avatar was pretty impressive. Eventually high quality renders of people and products (and landscapes?) will match photography for content creation. There are already programs that can dial up a person to specification, and changing clothing/hairstyles/accessories will be a breeze. It's only a matter of time.

Take a look at

this tutorial

by Olivier Ponsonnet. I think the last example is particularly impressive.

You may find an episode of the WNYC radio show On The Media instructive on this question.  It was called The Uncanny Valley, and it discussed the problem of CGI getting too close to the real thing and the way we react to it.  I remember being a little unnerved by the human characters in Shrek.  I was interested to learn that they were made less human looking because of the reaction they got from test audiences.

The uncanny valley problem is mostly an issue with moving images, because the way a person moves is as important as how they look in determining 'realism'. Shouldn't be a problem for still images.

We spend so much time on Photoshop making people look unreal, that now our perception is so screwed up that we think CGI looks real!

It does not, it looks like a very well done computer graphic but a computer graphic non-the-less.

Avatar was a motion picture. Our eyes are much more forgiving of detail on objects in motion.
A still image is meant to be dwelt upon and studied. Computer generated images of people just can't cut it yet.

Will they ever? Probably. But it's a world I don't want to live in.
I think there will be a huge backlash to it someday.
Just as the hippies of yesteryear rejected the social constructs of their day and helped reshape the way western civilization lives now.
So too, I believe that our synthetically created worlds will be rejected.

There has already been some of that happening.
There has been some small outcry about how perfect 'shopped' models look in magazines which in turn makes our daughters feel as if they are not good enough.

ETA: and when it does take over Microstock, expect to be paid 5% per download.
After all, you did not have to hire a model or a MUA or a stylist or a...