Method, apparatus and system for generating a feature vector

A method of generating a feature vector for an image is disclosed. Values are determined 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. A periodic sequence of the determined values is determined based on an order of the plurality of points. The periodic sequence is 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. The feature vector for one of the points is generated from a frequency domain representation of the periodic sequence, the feature vector being invariant to rotation with respect to the plurality of points.