Searching for photos online and using them responsibly and legally can be a lesson on its own that you may not all have time to delve into with your students, so here are a few sites and places to search for royalty free images that may be used without permission of the original owner.
Photos for Class: [ http://www.photosforclass.com/ ]
All search results are school appropriate, and each photo comes with the citation shown on the photo file. All photos are licensed for public use.
StockSnap [ https://stocksnap.io/ ] and Unsplash [ https://unsplash.com/ ]
There are plenty of sites like these, but these two both offer all free, high quality photos that may be used/downloaded/edited without permission.
Using Google images [ https://images.google.com/ ] is not as streamlined, but Creative Commons licensed photos may also be found. After searching for a photo, click “Tools” near the top of the search results. Then click ‘Usage Rights”, and then “Labeled for reuse with modification.”
This website gives even more websites to use and talks about why this is an important subject to talk about with your students. It also addresses giving attribution to the photographer and when it is necessary.