Short snippets of a teacher, even just explaining something, can, and have, been shared.
Yes but that is from their phones I assume.
In general we live in a world where everything is recorded. As soon as the children leave the school they are likely to be on CCTV and they will be recording each other all the time. The teenagers will be doing this sometimes when drunk or high, sometimes when naked , sometimes without permission.
For school teaching, the way we record lessons clearly needs careful thought. But I don’t think we can say a blanket no.