Evaluation of invariant models for dolphin photo-identification

Abstract

Individual identification of dolphins is of much interest to marine mammologists. Natural markings and notches on the trailing edge of the dorsal fin provide an almost unique signature within a study population for individual recognition. The dorsal fin is an almost rigid, planar object, and, as a result, the problem boils down to planar curve matching. Invariants under three groups of similarity, affine and projective transformations are examined in this paper. Three families of differential, algebraic and semi-differential invariants are studied and evaluated for their applicability and performance in dolphin identification from photographs. It is observed that, under practical conditions, for smooth quasi-rigid curves like the trailing edge of the dorsal fin, curvature-based matching methods outperform almost all of the other techniques which offer a higher level of invariance.