1. A method of generating an image descriptor for use in image processing, the method comprising: filtering image data to provide orientation data and energy data; generating a first set of global information and local information for the orientation data and a second set of global information and local information for the energy data; extracting descriptors from the respective sets of global information and local information associated with the orientation data and the energy data; combining the descriptors associated with the orientation data and the descriptors associated with the energy data to form an image descriptor.