MorgueFile

http://www.morguefile.com/

High Resolution images for all your needs!

Pexels

https://www.pexels.com/

The pictures are free for personal and even for commercial use. You can modify, copy and distribute the photos. All without asking for permission or setting a link to the source. So that attribution is not required.

GRATISOGRAPHY

http://www.gratisography.com/

Free high-resolution pictures you can use on your personal and commercial projects.
Click on an image to download the high-resolution version. New awesome pictures added weekly!

Picography

http://picography.co/

Free hi-resolution photos. Use them however you like.

Magdeleine

http://magdeleine.co/license/cc0/

More than 3600 photos that are Free to use and ready for instant download. Their categories include nature, city and architecture, people, animals, food, technology, objects and abstract art.