Negative Space has free stock images that are released under the CCO license. The images can be used in personal...
Superfamous has super great textures inspired by nature. There is a set of high resolution images, that have been released...
For personal or commercial use, PhotoCollections.io has images available for download and published with the Creative Commons license.
Skitter Photo has a large collection of free images to use for personal and commercial use.
A good sized collection of stock images to choose from. The images are also allowed for commercial use.
