Due to the high availability of public domain images, the Images category only shows these, as there's no need to look elsewhere or use more restrictive licenses. All of these are Creative Commons Zero (CC0) or otherwise public domain.

There are countless other places to find images without restrictions, but these are my favorites. If you can't find what you're looking for on this list, here are two other lists by others that can help.
WP Tavern's list of 13 sources for Public Domain/CC0 images
Sellfy's list of 43+ Unique Places to Find Remarkable Free Photos