Stock footage, otherwise known as archive footage, is used for many different purposes. A lot of film is shot in the making of a movie or shot but it's not all included in what the audience sees. Sometimes a lot is cut, or sometimes actors need many takes to get the scene right. There are mistakes and long shots for the background. Rather than throw this all away, studios tend to save it all for years. The property rights on this film can differ depending on companies, contracts, and content.

There are several reasons why this is done. The first is akin to the definition above; more film is shot than is needed. Often the film is kept just in case it is ever needed. Many films in production put out a "behind-the-scenes" look at the upcoming movie. A lot of footage is used here so the audience can get a glimpse at the movie without too much being given away.

Since the birth of the DVD, stock footage makes for nice special features. Bloopers are a great way to get to know the cast and footage can let the audience know how certain stunts or big moments were really done. It can give clues to the what it might be like to be on the set. Many fans of movies watch these special features religiously and would do anything to get their hands on all of the stock footage from a film.

Big historical moments can be considered archive footage, too, if they are video taped. Most of this is public domain or the property of the government. It makes it easy when someone wants to make a biopic; they then have all this real footage of their subject at their disposal. It adds credibility to the film because it shows the filmmaker did his or her research.

All iconic moments are subject to being archive footage - even scenes from other movies. In fact, one might say that classic movies are especially qualified to be stock footage. Some shows are comprised of people sitting around and discussing famous movies, making lists and countdowns, and showing clips. This allows the audience at home to see what they are talking about if the audience member hasn't seen that particular movie.

It doesn't have to be a large, iconic moment, though. Much of the footage is used as background in the movie and is scarcely noticed by the audience. Many films can use the same shot of a landscape or the same background for someone driving. Thematically the footage can be good to subtly demonstrate the atmosphere of the film.

Though it does not draw attention to itself, this type of stock footage is very important to the subtext of the movie. It can tell an audience a lot. If the movie is done well, the passing footage in the background can give subtle clues to what's going to happen or to the characters' inner thoughts. If a movie is not carefully thought about and planned, it is easily noticed through shoddy details like background footage poorly matched to the current action.

The stock film footage can also become very useful for shows with low budgets. If a similar action happens a couple of times in a film, the film makers can get away with showing the same stock footage video from an early part of the movie. Children's shows do this constantly since kids tend not to notice.