Abstract: The identity of horses is established by optically scanning the four "chestnuts" located on the insides of their legs to generate digital numbers corresponding to the width, height and area of each chestnut. These numbers are encoded digitally with an application number assigned to the individual horse and the serial number of the equipment performing the scan to produce a code which is then stored on tape within a tape recorder. The code is thereafter transmitted to a central data bank for future reference so that the identity of the horse can be subsequently checked to prevent fraudulent and mistaken substitution of horses. The apparatus and method is also useful in identifying lost horses and in controlling theft and disease.