Creative Commons is an organization that has made it much easier to share knowledge and creativity around the world. The organization develops, supports and stewards legal and technical infrastructure that maximizes digital creativity, sharing and innovation.
There is no registration process involved in the use of Creative Commons licenses: simply select which of the available licenses best meets your goals and objectives, then mark your work in a manner that lets people know that you have chosen to release that work under the terms of that license. Each license allows you to keep your copyright but allows other people to copy and distribute your work provided they give you credit for that work and that they obey the other conditions that are specified in the terms of the license you choose.
"All Creative Commons licenses have many important features in common. Every license helps creators — we call them licensors if they use our tools — retain copyright while allowing others to copy, distribute, and make some uses of their work — at least non-commercially. Every Creative Commons license also ensures licensors get the credit for their work they deserve. Every Creative Commons license works around the world and lasts as long as applicable copyright lasts (because they are built on copyright). These common features serve as the baseline, on top of which licensors can choose to grant additional permissions when deciding how they want their work to be used.
A Creative Commons licensee answers a few simple questions on the path to choosing a license — first, do I want to allow commercial use or not, and then second, do I want to allow derivative works or not? If a licensee decides to allow derivative works, she may also choose to require that anyone who uses the work — we call them licensors — to make that new work available under the same license terms. We call this idea “ShareAlike” and it is one of the mechanisms that (if chosen) helps the digital commons grow over time. ShareAlike is inspired by the GNU General Public License, used by many free and open source software projects.
Our licenses do not affect freedoms that the law grants to users of creative works otherwise protected by copyright, such as exceptions and limitations to copyright law like fair dealing. Creative Commons licenses require licensors to get permission to do any of the things with a work that the law reserves exclusively to a licensor and that the license does not expressly allow. Licensees must credit the licensor, keep copyright notices intact on all copies of the work, and link to the license from copies of the work. Licensors cannot use technological measures to restrict access to the work by others." - from the Creative Commons website and licensed under the Creative Commons Attribution 3.0 License, of course.
The majority of photos found on TheArmchairExplorer.com are licensed for use under one or another of the Creative Commons Licenses. Some photos are sourced from governmental projects where the photos are in the Public Domain. Wherever possible, I attribute those public domain photos to that source and to the actual photographer (if that name is available). Some of the public domain photos are from the Wikimedia Commons repository and I attribute those as best I can. Same for the photos from Flickr. Some of the maps are from Cartesia MapArt US Terrain, some from National Geographic Topo! I attribute those, too, on the appropriate pages.