Pixabay is a Public Domain free image repository for finding and sharing images. 

Flickr is an openly licensed image bank for locating and uploading images to share. 

Wikipedia Commons is an open platform for finding and sharing open information, including photos.

FreePixels is a repository for the free downloading and uploading of stock images.

Public Domain Photos houses large collections of photos and clipart no longer under copyright.

Every Stock Photo contains openly licensed and public domain photos to use and share.