99.9% of the images belong to someone. just taking it, for your own use is not cool.
Would you, as a photographer, be happy to see your pic's all over the internet, without, at BARE minimum, even your name? There are websites, such as sxc.hu that you can get images at no cost, but most require a link back to the photographer.
We have, on a few occassions asked website owners to either remove an image, or give credit.
There are no police, but there is such a thing as copyright infringement, and conscience.