Here is a list of royalty free photo reference sites that you can use as an artist without breaking copyright law, but please be aware that some may have some requirements such as crediting and thanking the artist or posting your finished work. Please check with each individual site for their terms.
Royalty Free Photo Websites for Artists
http://deathtothestockphoto.com/ – subscribe for free and receive a package of 10 free photos every month
Photographic Reference for Artists (PRA)
Art Reference Team (ART)
Wendy’s Photos for Creatives (Photos by Wendy Sinclair)
Lengyel Wildlife Art Reference Photos
https://www.flickr.com/creativecommons/ – You can search Flickr for the creative commons pictures, not all of them are creative commons.
You can search this in google images – “This work is licensed under a Creative Commons” site:deviantart.com
In google images: Select ‘Usage Rights’ and then choose ‘Labeled for Reuse’ – not all of these photographs are Royalty Free.
Paid Royalty Free Websites
You can use a picture for a small fee. Please check with each individual site for their terms.
If You Still Need More . . .
Here are some more resources on this blog post by Art Tutor:
Last updated 5/28/2017 by Cecilia Kinzie from the CP4B group: