If you haven't done the challenge yet, please don't read the examples I give below in silver text. If you don't understand what I mean, highlight the big gray empty area with your mouse.
Examples? Well, just looking at the grass picture, I could tell it was CG because of the perfectness of the water droplets. On the picture of the face, there is almost no definition to the lips, and the way the skin on the nostril area is perfectly round, with bad shading gives it away. As for the fork and the spoon, I didn't even need to zoom in for details, because it just looks fake. Especially the fork, which looks like it has wood grain. The only ones that really tricked me were the nails and the glasses of water.
Chris
I love CG. I had a couple of tapes full of nothing but CG animations. They were called The Mind's Eye and Beyond the Mind's Eye. I have this other one called Animation Dreams, but that one kinda sucks.