Is taking a video or photograph of another person illegal?
It depends. Generally, whether taking video or a photograph of another person without his/her consent or knowledge is legal or illegal may depend on whether the subject of the video or photograph had a reasonable expectation of privacy in the place where video or photograph was taken. A “reasonable expectation of privacy” generally exists if you are in a place where an average person would expect to not be seen or spied on.* For example, if you are in a public place, you may not have a reasonable expectation of privacy, but if you are in your bedroom or a public restroom stall you generally would.
* See Katz v. United States, 389 U.S. 347 (1967) (noting that “what a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.”)