Most stock footage has some form of copyright protection, except for Public Domain footage that allows you to use it as you please. Also look into "Creative Commons" licensing for a no cost way of using somebody else's footage.
The Best Kind of Stock Footage
One of the greatest things a home digital video producer can hear when he is looking for stock video footage is the words "Public Domain." Since copyright law is so restrictive and confusing to interpret it is wonderful when you are able to find footage that is not subject to that kind of legal restriction. Though much of the footage that fits into this category will be copyrighted, there is some that is considered as being in the Public Domain.
How To Know
Public Domain is any artistic creation, which would be referred to as Intellectual Property that has no ownership or control, or that ownership and control has been voluntarily given up. They are considered public and can be used by anyone for any purpose without the need to get approval from any outside party. If the work was produced by the United States government it is not eligible for copyright protection, and therefore is in the Public Domain. This means that any video or photo that is produced by a government agency, such as the military or judicial departments, can be used freely. This does not, however, include work produced by government contractors. Another type of footage that is in the Public Domain is any video or photo that was created before 1989 and does not have a copyright notice on it. Anything produced in 1989 or later was automatically given copyright protection once it entered a “tangible medium." Any work that was published before 1923 is automatically in the Public Domain because its term of copyright has expired. This would include great historical photos and silent films, but not anything that can be used to portray more contemporary images. Current copyright does not expire until the entire term of the author’s life plus seventy more years, so most contemporary works are going to be protected for quite some time.