Free image resources?
Some I know:
https://pdimagearchive.org
https://unsplash.com/ - filter results for 'free' eg:
https://unsplash.com/s/photos/ostrich?license=free
https://pixabay.com
Also has vector graphics, not really explored this site
https://pixabay.com/vectors/
You can also use Flickr to find free-to-use images, sometimes these require attribution or whatever
https://www.flickr.com