1. A method of capturing and processing images of an area of terrain, the method comprising: for each of a plurality of time-steps within a time period, using each of a plurality of cameras in a camera array, generating an image of a respective portion of terrain, wherein the cameras in the camera array have substantially fixed positions relative to each other, and the portions of terrain are such that a whole of an area of terrain has been imaged by an end of the time period; selecting a subset of the generated images such that the whole of the terrain is covered by the portions of the terrain in the images in the subset; and for an image not in the subset, if an object of interest is in that image, extracting a sub-image containing the object of interest from that image.