Given Google is in the US, I'm going by US based laws:
It is legal to photograph or videotape anything and anyone on any public property.
Photographing private property from within the public domain is legal, with the exception of an area that is generally regarded as private, such as a bedroom, bathroom, or hotel room. In some states, there is no definition of "private," in which case, there is a general expectation of privacy. Should the subjects not attempt to conceal their private affairs, their actions immediately become public to a photographer using an average lens or video camera.
If you are in a city park for what ever reason, I can pop up a camera and video tape you as much as I want.