Image Sources and The Law: Definitions

Copyrighted Photos- You own the rights to that photo and it gives your original work protection from other people using it without permission.
http://www.kodak.com/global/en/consumer/doingMore/copyright.shtml

Stock Photos- A photo that already exists and can be purchased for use instead of having another photo specifically made.
http://www.sxc.hu/

Public Domain Photos- large collections of free or inexpensive photos.
http://pdphoto.org/

Royalty Free Photos- Any sort of art work that can be used, but usually for a specific amount of money and only certain ways, for example they may not be distributed to a third party if the terms of usage say not to. Also, the artist hold all rights.
http://www.fotosearch.com/

Model Release For Photos- When using pictures that contain clearly recognizable faces of people, a model release protects you against legal claims by the persons in the photo. These are usually used for advertisments and commercials.
http://www.danheller.com/model-release.html#1