"Free high quality photos you can use everywhere."
From their photo license web page:
"All photos on Pexels are under the Creative Commons Zero (CC0) license. This means you can copy, modify, distribute and perform the photos. The pictures are free for personal and even for commercial use. All without asking for permission or setting a link to the source. So attribution is not required. All in all the photos are completely free to be used for any legal purpose.
The CC0 license was released by the non-profit organization Creative Commons. Get more information about the license on the official license page.
RestrictionsIdentifiable people may not appear in a bad light or in a way that they may find offensive, unless they give their consent.
Do not suggest endorsement of products, services, etc. by displayed people or organizations. For example: do not place an image of Apple in a way that suggests Apple would recommend your product.
About Us
Currently we cover over 850 photos. Every week we add 30 new photos. All photos are hand-picked from free image sources. We make sure that all added pictures are high-quality and under the CC0 license. We only add photos from reliable sources like Unsplash, Gratisography or Little Visuals.
You have questions about the license or anything else related to Pexels? Then write us an email: info@pexels.com"
http://www.pexels.com/