Save this link - you will want it: https://search.openverse.engineering/.

Yes, pictures from Wikipedia and Wikimedia can be used on your Moodle site. They hold a large collection of public domain and Creative Commons licensed images (23 million). Similarly, the image site Flickr holds many images whose copyright means they can be used. These sites can be searched individually, however the openverse search tool (previously called CCsearch) searches all these sites as well as a whole range of other sites.  Thus, in this short guide to copyright, we are only going to look at how to use and attribute images found via Creative Commons.

A list of the collections included in Creative Commons can be seen here.

By the way, notice how dull this page appears without an image.