Photography is something that a lot of people treat as a profession if they are getting paid to do it. In order to gain credibility, photography licensing is very important. Not only does it help legitimize everything, but it helps for people to make money as well.
The way licensing works is that photographer will give up special rights to a client that they will then be able to use the image for their own use. Sometimes, those rights allow people to use the photo at any time. In other scenarios, it could only be for a set amount of time before it expires. The pricing obviously varies depending on each individual photographer, but it is something to keep in mind when examining everything. So many people are under the assumption that photographs are available for free if found online.