Abstract: In various embodiments, the present invention is directed to photothermal-responsive melanin-based nanocomposites comprising a plurality of natural or synthetic melanin nanoparticles distributed with a polymer matrix suitable for use in anti-counterfeiting, photothermal responsive-communication, sensors, and heat management, among other applications. In some embodiments, the present invention will be an ink, paint, or other coating comprising the photothermal-responsive melanin-based nanocomposites. In some embodiments, the present invention is directed to a written message or design comprising one or more of the photothermal-responsive melanin-based nanocomposites. In some of these embodiments, the written message or design will be comprised of two ore more of the photothermal-responsive melanin-based nanocomposites having different concentrations of natural or synthetic melanin nanoparticles.