Do you need consent for people in the background?
Question: When filming a documentary you always film people in the backgrounds... on the streets, on a school, at the market... are those hundreds of people crossing the frame a problem as long as they will never consent to the camera?
Technically, anyone who can be seen (clearly) in your documentary needs to give you their permission in writing using a "talent release form". If not, you would need to blur them out. However, I suggest you simply use some common sense. If you are filming a highly controversial and negative film and show people that represents them in a negative way, they are not going to like that and they could sue you. But if they are shown in a very vague way as part of a neutral or positive frame of reference where they are not easily recognizable, then you should be okay.
Here is a similar question that came into our site which may help you:Shooting With a Remote Helicopter Cam
Also read this article about copyright & legal issues:Legal, Consent and Copyright Issues
One last point: If your documentary ends up getting picked up for broadcast on television, they will often require you to buy "Omissions and Errors Insurance" which covers you in case someone tries to sue you. And broadcasters and distributors will require that you have releases on anyone that is shown prominently in your film.
Please understand that I am not a lawyer. I am simply giving you advice based on my 20-years experience as a documentary and video producer.
Do you have a better answer for this question? Please leave comments below. Recommended Resource!
The Pocket Lawyer for Filmmakers, Second Edition:
A Legal Toolkit for Independent Producers