If you are in a public area, can you take photos or videos of other people? This question is answered primarily by reference to the Privacy Act 2020.
General Advice
If a person is an agency (such as running a one-person business) and collects personal information about an identifiable human being, the Act and its Privacy Principles apply. They govern your collection and use of that information, primarily by the purpose of its collection.
There is an exception under the Act if the personal information is collected by an individual in a private capacity in relation to their personal affairs (s 27).
This suggests that taking photos or videos in a public place is permitted. But the exception is limited. If the personal information is collected, used, or disclosed in a way which is highly offensive to a reasonable person then the exception does not apply.
The standard can be approached in this way. Place yourself in the position of the person whose personal information is being collected by you. If you were them, would you think that the collection of information about you would be in breach of your reasonable expectations of privacy such that the collection is not trivial or merely triggering but is distressing, humiliating or genuinely offensive to you?”
Much depends on the context.
You would expect that mental and physical health issues are likely to raise sensitivity. Is the person a child or otherwise vulnerable? How intimate or sensitive is the information? Did the person know that the information was being collected? Was the collection in a truly public place like a park or beach or in a space where there are likely to be access rules such as shopping malls, swimming pools, or doctors’ surgeries?
In any of those cases the risk of offense increases. The filming of an accident scene is likely to be highly offensive whereas the filming of a crime taking place is unlikely to meet that threshold.
Finally, note that there is a further exception for the news media in carrying on the reporting of news. The Privacy Act does not apply to the media (s8 (b)(x)) so if you are filmed in a public place and end up on TV you can only complain to the Broadcasting Standards Authority.
Overall, be cautious in taking photos or videos of other persons in a public place. Permission is a good principle to apply.