1. A method of estimating an angular position of a turning leaf in an image of a book, comprising the steps of: capturing a video image frame of the book; estimating a position of at least a first endpoint of a spine of the book; applying an edge detection operation to the video image frame of the book to generate an edge image; defining a first region having its lower boundary centred upon the first endpoint of the spine of the book; applying a Hough transform to the first region in the edge image to obtain a plurality of line estimates; rejecting line estimates that do not substantially intersect with an estimated endpoint of the spine of the book; for line estimates that are not rejected: detecting one or more clusters of angles of said line estimates with respect to the estimated endpoint of the spine of the book, and generating a respective average angle from each of the one or more clusters of angles; selecting a respective average angle from the respective average angles; and estimating the angular position of the turning leaf in the image of the book responsive to the selected average angle.