Alaska-based photographer Mark Meyer has written up an interesting piece examining the use of computer generated images in lieu of photography in advertising, marketing, and product development. In experimenting with Blender rendering software, Meyer realized that cg software is now cheap and easy enough to generate images that rival those of still life photographs. He writes:
For the first time in history, photography is about to lose control of its monopoly on affordable, convincing realism and it's time for us to understand that realism has never been the most important feature of the photograph...At the moment photography is still the most affordable means to quickly create realism in most applications with notable exceptions in large scale cinema productions and car advertising. But the two worlds are about to merge and a large part of the photography industry will be replaced by software.
For example, Meyer created the above image in Blender, simulating the fluid dynamics that would've been challenging for a photographer to perfectly time and capture in a studio. On the computer, Meyer can tweak the model, lighting, and "camera" angle without consequence or cost. And while professional CG artists may still charge as much as a studio photographer, rendering time and costs for cg are going down while quality is increasing over time.
But I don't think photographers have much to fear even in the long run--photography and cg aren't mutually exclusive. In fact, as Meyer can probably attest, his skills as a photographer contributed a lot to his ability to generate that render. Cameras and computers are both tools that required the trained eye to utilize properly; a computer graphics artist with no understanding of light isn't going to create a better image than an experienced photographer. They might be able create a "good enough" image faster, but not necessarily more convincing. One example that comes to mind is the use of photography in the cross section photos in the Modernist Cuisine books. These were images that likely could have been more cheaply created with cg, but the book's authors chose to take on the challenge to taking real photos for authenticity. I've seen these physical cutaways in person and the fact that they're real tangible objects makes the Modernist Cuisine books more credible and impressive.
Even if we're just talking about commercial and still-life photography where cg images are more than passable, there's a disconnect between the artificial and the real. It reminds me of a Chinese proverb about painting legs on a snake: an artist can add unnecessary detail that ruins the gestalt of the work. With the precision and control offered by cg, artists are actually struggling to find that balance between too much detail and replicating the imperfections of reality. Chaos and spontaneity are difficult to simulate. As Meyer concludes, "it's not about the realism, but rather the fact that renderings and drawing can't bear witness in the way a photograph can. This is where photography distinguishes itself as a medium and it's time for photographers to embrace it."