Commercial Free Stock Photography:
https://www.pexels.com/ – All photos on Pexels are licensed under the Creative Commons Zero (CC0) license. This means the pictures are completely free to be used for any legal purpose including commercial.
https://pixabay.com/ – All images and videos on Pixabay are released free of copyrights under Creative Commons CC0. You may download, modify, distribute, and use them royalty free for anything you like, even in commercial applications. Attribution is not required.