YouTube takes copyright seriously! Here is a course they have about it: https://www.youtube.com/yt/about/copyright/#support-and-troubleshooting
Consequences for breaching copyright on YouTube include loss of the ability to post videos and removal of all videos and channels you have!
Recommended Free sites:
- Pixabay – Royalty Free CC0 Creative Commons
- Unsplash – Free for both commercial and non-commercial use. See this License
— Judith Dutill (@judithdutill) May 10, 2018