-copyfree- works that you can copy it freely without any permission(not so reliable)
-trade mark-A name, symbol, or other device identifying a product, officially registered and legally restricted to the use of the owner or manufacturer.
-creative commons- is a non-profit organization headquartered in Mountain View, California, United States devoted to expanding the range of creative works available for others to build upon legally and to share
-royalty free- is a term employed in negotiating the right to use creative content, such as photographs, video, or music
-gnu licensed- General Public License is a free, copyleft license for software and other kinds of works
-public domain- refers to works whose intellectual property rights have expired

