Copyrights

Copyrighted Photos
Definition: Copyright is a protection that covers published and unpublished literary, scientific and artistic works, whatever the form of expression, provided such works are fixed in a tangible or material form.

http://www.whatiscopyright.org/

Stock Photos
Definition: stock photography is not public domain. These images, although provided to you for free or a fee, are not being given to you in ownership. You are being allowed to use them if you comply with the owner's terms and conditions

http://www.whatiscopyright.org/

Public domain photos
Definition: graphic images (including web graphics, stock photos, logos and other digital art), writings, HTML, cascading style sheets, javascripts or anything else that has been placed in the public domain does not grant you the right to claim copyright to it just because you find it.
http://www.whatiscopyright.org/

Royalty free photos
Definition: This contrasts to rights managed images which are rented for a specific, one-time use at a price that is determined by the scope of that particular usage.
http://www.comstock.com/WEB/IHF/LICENSE/IHFLICENSERFDEF.ASP

Model Release for photos
Definition:a model release is a document that stipulates the terms under which one party may use pictures taken of another party.

http://www.danheller.com/model-release