When is it necessary to get release forms when filming in a public place, such as a beach, park, or street? If people's faces are visible in the background, do you need release forms?
Legally yes. It really depends why you're shooting. Where will it be shown/broadcast. It is acceptable to post a sign in public places that states by entering the area you are giving your permission to appear on camera. But, you also then need to shoot the sign and make sure it is clear that it is in a highly visible location. If you have a PA you can even have them hold it in clear sight where you're shooting. Technically anyone appearing on camera (that is recognizable) needs to give their permission to be shown. I do NOT know anything thing about the rules when it comes to news coverage. I'm only familiar with entertainment rights.
As Stu Maschwitz has said, you may need a permit to film on a city street, but you don't need one to put your sticks on a pickup truck on the side of that street, or film out of a van, etc.