1. A method of correlating an image of a feature of interest, comprising: acquiring a first image of a feature of interest; generating a learned circlet image from the first image, wherein a circlet is defined as a compact angle representation expressing, at a given pixel comprised in the first image, the direction of change of pixel intensity; saving one or more sets of learned circlets corresponding to one or more selected probes; acquiring a second image of the feature of interest; generating a target circlet image from the second image; and correlating the learned circlet image and the target circlet image.