1. A method of generating a feature vector for an image, the method comprising: determining values from a plurality of points in a region of the image, each of the values being determined using at least two of the plurality of points; determining a periodic sequence of the determined values based on an order of the plurality of points, the periodic sequence being phase variant to a starting point of the ordered plurality of points, the order of the plurality of points being determined according to a predetermined rule; and generating the feature vector for one of the points from a frequency domain representation of the periodic sequence, the feature vector being invariant to rotation with respect to the plurality of points.