Recently I have been asked why I have a large copyright symbol over the photos on my website. I have been told that it is a bit distracting.
These images are from projects and jobs that my clients have paid me to take. So to ensure the image are not taken from the site and use elsewhere without my permission and to keep their value for my clients I have this symbol covering the center of the photo. Copyright infringement of photos online is a huge problem. Especially when one is working as a professional photographer. If one of my photos is taken from my website and used all over the web it is immensely devalued for my clients, who have paid for my services and the exclusivity of the image itself. I wouldn't be surprised if my client didn't hire me again after a scenario like this.
Which is one of reasons why I rarely ever post an image on Facebook. Facebook does not consider or care about the rights of the photographer or owner of the photographs posted. One reason they don't want to manage copyright infringement is that it is too laborious and expensive to worry about. But for us who's livelihood is the photographic images we produce it is important, as well as the overall service provided.
If you think an image online has been produced by a working photographer/artist please do not use it inappropriately. Contact the photographer/artist and ask to use it. Most of the time they will not have a problem for you to use it, making sure to give the credit to them.