creative commons:  

   Creative Commons is a nonprofit organisation dedicated to building a globally-accessible public commons of knowledge and culture. We make it easier for people to share their creative and academic work, as well as to access and build upon the work of others. By helping people and organisations share knowledge and creativity, we aim to build a more equitable, accessible, and innovative world.

 Attribution (by)

All CC licenses require that others who use your work in any way must give you credit the way you request, but not in a way that suggests you endorse them or their use. If they want to use your work without giving you credit or for endorsement purposes, they must get your permission first.

 ShareAlike (sa)

You let others copy, distribute, display, perform, and modify your work, as long as they distribute any modified work on the same terms. If they want to distribute modified works under other terms, they must get your permission first.

 NonCommercial (nc)

You let others copy, distribute, display, perform, and (unless you have chosen NoDerivatives) modify and use your work for any purpose other than commercially unless they get your permission first.

 NoDerivatives (nd)

You let others copy, distribute, display and perform only original copies of your work. If they want to modify your work, they must get your permission first.