http://www.chabad.org/library/article_cdo/aid/912361/jewish/Chapter-Three.htm
Halacha 10:
It is forbidden to make decorative images of the human form alone. Therefore, it is forbidden to make human images with wood, cement, or stone. This [prohibition] applies when the image is protruding - for example, images and sculptures made in a hallway and the like. A person who makes such an image is [liable for] lashes.
In contrast, it is permitted to make human images that are engraved or painted - e.g., portraits, whether on wood or on stone - or that are part of a tapestry.
(I added the emphasis.)
Halacha 11:
The images of animals and other living beings - with the exception of men - and similarly, the images of trees, grasses, and the like may be fashioned. This applies even to images which protrude.
Note that there are some special cases for images of celestial objects (sun, moon, stars) and you should read the commentary at the bottom for details. Also there is a prohibition for the d'rakon animal (again, see the comments).