1. A system configured to uniquely identify individual subjects from a group of subjects, the system comprising: electronic memory for storing a plurality of records that correspond to a plurality of individual subjects from a plurality of species, wherein the records include features of one or more characteristics of the corresponding subjects, and wherein the plurality of records comprise: a first record that corresponds to a first subject, wherein the first subject is from a first species, and wherein the first record includes: a first identifier that uniquely identifies the first subject from the other subjects, and features of a first external characteristic of the first subject that distinguish the first subject from other members of the first species, and a second record that corresponds to a second subject, wherein the second subject is from a second species that is different from the first species, and wherein the second record includes: a second identifier that uniquely identifies the second subject from the other subjects, and features of a second external characteristic of the second subject that distinguish the second subject from other members of the second species, where in the second external characteristic is different from the first external characteristic; and a processor for obtaining a digital image of a current subject that captures a characteristic of the current subject, determining a species of the current subject, and determining an identity of the current subject based on a comparison of features of the characteristic captured in the digital image and features of the characteristic stored in records corresponding to subjects from the same species as the current subject.