Yeah, never a good idea to use anyone else's work. I actually got into trouble years ago with Paramount Pictures and almost got my account deleted. Now I get all my music on this site, it's not cheap, but if you do YouTube seriously or are making games it's well worth it.
https://artlist.io/
If you don't want to pay, you can check this site, it's all basically free open source (they have music, photos, etc.)
https://pixabay.com/