Flickr works as a community. You upload photos, people find them and ask you if they can use them. You get feedback without advertising them or something like that.

Sometimes however people use your pictures without letting you know. This happens of course when you attach a proper license to your photos. This happened to one of my 24c3 photos. The german newspaper »Die Zeit« used this one on their website in this article.

I think flickr is amazing in many aspects as it is one of the few web communities that are useful.