An ink and ink set characterized in that both a combination of a specific wetting agent, penetrating agent, and water-soluble organic solvent and use of surfactant, particularly fluorine surfactant are enabled by using water dispersion in which polymer fine particles contain coloring material. By reading the individual identification code of an animal from this digital picture, it becomes possible to quickly and accurately manage pictures of animals. The second laser beam propagates parallel to the first laser beam after leaving the first crystal. The heat sink may be moved from the first to the second operable position to facilitate access to electrical contacts proximal the heat-generating electronic component.