1. A method of book leaf tracking, comprising: receiving a video image comprising a book; estimating a current position and orientation of the book within the video image in response to a fiduciary marker of the book visible in the video image; estimating visibility of one or more predetermined features of the book; calculating a range of leaf turning angles that is consistent with the estimated visibility of at least one of the predetermined features of the book for the estimated current position and orientation of the book; and estimating an angle of a turning leaf of the book responsive to the calculated range.