It would still be rude and violate widely held standards for personal space and privacy. Never forget that legal and appropriate are very different things.

IANAL.

In the USA, it depends on jurisdiction and the circumstances. For example, CA is a "two-party consent" state, meaning that to record another party requires their knowledge and consent in some circumstances. This case (a camera in the back of an airline seat) is a bit on the line: the space isn't terribly private (it's a row of seats on an airline), yet a private conversation might be had in a low voice between two people, who did not see, or do not recognize, and were not told that there is a camera pointed right at them.

I do not know if this is a violation of two-party consent. It might not be.

Commercial use of a photo or video with an identifiable person requires permission (model release forms and stuff). I'm sure that airlines would argue that any data they use for commercial purposes are anonymous (despite you know aving video and name/seat/camera correspondence).

In the UK, this sort of thing (putting camera right in your face against your wishes, more than once) might be considered harassment, even in a public place.