These are some of my favorite places to find quality photographs for free:
- Wikimedia Commons: the picture archive of Wikipedia offers millions of photographs online. A great deal of them are available under one or another creative commons license. Licensing is clearly stated.
- pexels.com: all photographs are available under Creative Commons Public Domain (CC0) license. Pictures are aggregated from other sources too.
- pixabay.com: all pictures (photographs, illustrations, vector graphics, video) are available under Creative Commons Public Domain (CC0) license. Pictures are aggregated. You need to log in to have access to full resolution artwork or SVG-files for vector art.
- pxhere.com: all photographs under Creative Commons Public Domain (CC0) license. Also comes with a color swatch to show what palette dominates the picture. Login is required to download.
- freephotos.cc: aggregation of many other sites, mostly CC0
If you're looking for even more links - I haven't verified these myself, but it looks like a nice list... https://wiht.co/freestockimageslist
A nice article on using images in blog articles, was written by Mathew Dixon.