Copyright is a very big deal. If you violate copyright claims the person you stole from could sue you for copyright. There are sights that give you photos, videos, memes for free. If you get permission all copyright drops. Some sites that you could use are:
Unsplash
Pixabay
Pexels
Photos For Class
Openclipart
Pics4Learning.

Most of these sites you do not have to sign up for. But some sites specialize in different things. Some have photos but not videos some have the opposite. Copyright is when you create something and you don’t want people using it you could copyright the photo or video that nobody could use that photo or video.