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, 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 record includes: features of a first external characteristic of the first subject that distinguish the first subject from other subjects of the plurality of individual subjects, and a second record that corresponds to a second subject, wherein the second record includes: features of a second external characteristic of the second subject that distinguish the second subject from other subjects of the plurality of individual subjects, where in the second external characteristic is different from the first external characteristic; and a processor configured to: obtain a digital image of a current subject that captures a characteristic of the current subject; determine 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 plurality of individual subjects.