Stone Tower
FreeImages.com is a terrific site to find images that you can use for free. Always read the licence agreement to see if you need to credit the photographer.
Free Images allows you to use images without credit unless you are using them in an editorial setting.
However, it only takes a minute to add a photo credit, and if the photographer is giving their work away for free in an effort to promote their work, it’s a courtesy that is easy to follow.