These three images were submitted for our photo club's monthly contest. The red Columbine was entered into the nature category.
The second two images were entered into the open category. The ducks are sitting on what is cut grass, so the "hand of man" is evident and therefore they do not qualify as nature, at least for our purposes.
The butterfly image was taken in a butterfly house. Like animals at a zoo, this does not quality as a nature photograph either.
Eastern Red Columbine
Getting Your Ducks in a Row