Below are some sites with available photos, video and audio. Many of them are licensed by Creative Commons.
Be sure to credit content with Creative Commons licenses. Learn more here.
Unsplash (Creative Commons Photos)
Openverse (Creative Commons Photos, Audio)
Flickr (Creative Commons works)
Google Images (be sure to change license to Creative Commons)
Flickr 360 photos (courtesy of Brendan Burke)
Flickr Equi-rectangular photos (courtesy of Brendan Burke)