Locating an affine/projective invariant identifier patch on an image

Single view recognition is encountered in many photo-identification applications. Often a query image is retrieved by searching a database of previously identified images. Important markings and patterns are often located in a particular area of the object. This paper presents a method to locate an invariant patch on an image using few points in correspondence and few invariant ratios. Computation of ratios is simple and intuitive both geometrically and analytically. Once ratios are computed for an appropriate multilateral patch, the same ratios can be used on other images to locate the same identifier patch. In particular, this method is deployed to obtain the same area of interest on spotted dolphins.