I have marked all my images as Attribution-NonCommercial-NoDerivs License.
I find it more than a little annoying when I see pictures which I've taken online with no attribution. Or worse, I have found some with a mark indicating they are owned by that website. These are obviously people with no scruples. For example, here's a picture taken in Wadi Rum in Jordan in the early 1980's. I added this image, right here, in my eJournal and images in 2004. It's a desert security policeman with his camel.
Here are some examples of this image either modified or used without attribution. How very unprofessional! It's not exactly theft, but it tastes nearly the same.