Search for copyright free images. (Google custom search).
There are many more copyright free images available from sites on this list.
(Note this is a Diigo list, Diigo makes it easy to store and organise your bookmarks online which means you can access them wherever you are).
Note that it is usually a requirement to give correct attribution when you use a copyright free image. The above image was found by searching on flower in a Google custom search for copyright free images.
There is a comprehensive tutorial here from JISC Digital Media.