Copyright can be legally a tricky subject and there is a lot of misunderstanding around the laws, especially with regards to fair usage – e.g if you were to use copyrighted material in a review of the subject to illustrate a point or for parody purposes.
The Mountain below has the following copyrights:
Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made
NonCommercial — You may not use the material for commercial purposes.
NoDerivatives — If you remix, transform, or build upon the material, you may not distribute the modified material.
No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.

“mountain” by barnyz is licensed under CC BY-NC-ND 2.0
This Dam image below has the following copyright:
Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made
NonCommercial — You may not use the material for commercial purposes.
NoDerivatives — If you remix, transform, or build upon the material, you may not distribute the modified material.
No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.

“Hoover Dam 2005” by stevencko is licensed under CC BY-NC-ND 2.0