If I had a great idea, photo, song (that will never happen), video, or anything else that would warrant copyrighting, how I wanted it used would determine how I would license. If I thought it had the potential to be a big money maker, then I definitely would use the most restrictive licenses.
According Creative Commons, there are six level of license. They are, 1) Attribution, 2) Attribution-ShareAlike, 3) Attribution-NoDerivs, 4) Attribution-NonCommercial, 5) Attribution-NonCommercial-ShareAlike and 6) Attribution-NonCommercial-NoDerivs.
While searching for a photo to use here I found this link with public domain pictures. I was able to find many photos that are free for commercial and personal use. They only ask if you use one of their photos that you link back to their site. So, I chose this picture. It reminded me my daffodils that are blooming in my flower garden.
I think the photographer chose to share his photo on this site to gain exposure and popularity. The information on the website says this will help with your photographic and graphic skills.