IM Free provides a curated overview of freely available photos, all available for commercial use. All photos are thoroughly grouped and tagged, and usually released under a Creative Commons license. Overall, there are literally thousands of available items which you can use right away. And if you need even more pictures, Gratisography, Unsplash andPicjumbo are further resources worth looking into, with a growing collection of free high-resolution pictures that you can use for commercial and private projects. Alternatively, you could use Google CC Image Search as well, of course.