How To Use Stock Footage to Set the Scene
Using stock footage to set a scene is convenient visual shorthand, whether for fictional or documentary purposes, and a cheap alternative to location shooting. It is a technique nearly as old as filmmaking itself, so viewers will usually accept it without question. It can be jarring if your stock footage doesn't look like your original footage; if so, you can sometimes remedy this problem with a creative approach.
Step 1: Finding Stock Footage
You can license stock footage from numerous vendors on and off the web. Much of it is available royalty-free; all you have to pay is a one-time license fee. Some footage is "rights managed," which means the usage fee is negotiated based on how the footage is going to be used. You can generally find simple images such as landscapes for a low one-time fee. Check government archives as well; footage shot for US government productions generally falls into the public domain and is available without a fee.
Step 2: Common Uses
You'll normally use stock footage to set the scene when location shooting would be too expensive or otherwise unfeasible, and original footage is not necessary to convey your intent. For example, if you're making a documentary on cattle farming, you can use stock footage of cattle interchangeably with your original footage, since one cow pretty much looks like any other. Choose your footage carefully to be faithful to your scene: a family-owned dairy farm has a very different look and feel from a corporate factory farm.
The classic use of stock footage is for the establishing shot, an external image of where the following scene takes place. This is used for fiction, documentary and news alike, and can vary from a suburban house to a cityscape to the planet itself. An image at a far distance from the following scene, such as a cityscape, can look very different from the rest of your footage without drawing the viewers' attention away from the narrative. A shot of a building, on the other hand, should look similar to exterior footage used elsewhere in your film or video.
Step 3: Understanding Drawbacks
This illustrates the biggest danger of stock footage: if it looks too different from the rest of your footage, it can make your production appear cheap, drawing the viewer out of the narrative and putting your veracity in question. There are ways to compensate for this, such as filtering original footage in production or post-production to bring the lighting closer to the look of a necessary stock shot. If your finished piece will be shown on a big screen, make sure your stock footage is not noticeably grainy at that size.
Stock footage can also be used humorously or ironically, if the mood of your piece allows for it. A classic example is a shot of a character stubbing his toe, followed by NASA stock footage of Earth, overlaid with the sound of the character's scream. If your available stock footage is noticeably different from your original material, a humorous or ironic approach can quickly win over your audience. This works best if your piece has a light-hearted tone overall, but it can also provide welcome comic relief to more serious subjects if used correctly.