Object detection is often the first thing that computer vision systems do because it makes it possible to get more information about the object and the scene. Once an object instance, like a face, has been found, more information can be gathered, such as the ability to recognize the particular instance (for example, to recognize the subject's face), to track the object over an image sequence (for example, to track the face in a video), to extract more information about the object (for example, to figure out the subject's gender), and to infer the presence or location of other objects.