Creative Commons (CC) licenses allow a copyright holder to express the terms under which their works are available for others to use. The latest CC 4.0 licensing system is almost universally applicable, and it also takes into account catalogue and database protection. It consists of four criteria that can be combined to define the use of the work:
Attribution (BY) The author's name must be mentioned. When a work is used, the name or the pseudonym of the author must be mentioned. The Attribution BY license is always part of each license combination.
Non-commercial (NC) Not for commercial use. Permission from the copyright holder has to be obtained if the purpose of the use of the work yields economic benefit.
No Derivatives (ND) Not modifiable. Permission from the copyright holder is required, for any modification of the work or for using only parts of the work.
Share Alike (SA) Has to be shared with the same license, e.g. modified derivative work can only be shared with the same license as the original work.
By combining these four licences, six Creative Commons licenses are created:
Additionally, copyright-free material is marked as follows (copyright protection period expired, or all rights have been waived):
Public Domain / CC0
When using Creative Commons licensed material you must always include the author, license, and web address from which it was taken (except for Public Domain / CC0 license). The information can be added as a caption in the image, but if necessary, a picture list at the beginning or end of the material can be created.