1. A method of generating a keypoint descriptor for identifying an object in an image or in a sequence of images, the keypoint descriptor being substantially invariant to a transformation of the object in the image, wherein the method is performed using processing apparatus and includes: a) receiving object data representing an object for identification in an image; b) processing said object data to generate at least one basis function representing a feature having undergone at least one transformation or a transformation sequence across several consecutive frames, optionally using transformations that are out of the image plane to recognize objects from multiple views; c) modifying a prototype wavelet function based on said at least one basis function to generate a plurality of modified wavelet functions; d) comparing the plurality of modified wavelet functions with the at least one basis function; e) selecting a modified wavelet function of said plurality of modified wavelet functions based on the comparison of step d); and f) processing an input image or input orientation field according to said selected modified wavelet function to generate the keypoint descriptor, wherein the prototype wavelet function and the plurality of modified wavelet functions comprise a radial distance component and an azimuthal angle component, wherein the prototype wavelet function and the plurality of modified wavelet functions have the formula: 
 Ψ k ( d ,θ)= d n k −1 e −α k d ( n k −α k d ) ·(cos( m k θ)+ q x sin( m k θ)) where the term d n k −1 e −α k d (n k −α k d) is the radial distance component and the term (cos(m k θ)+q x , sin(m k θ)) is the azimuthal angle component, and where the term q x , denotes an imaginary unit.