The tattoo includes a QR code, which is basically a multi-dimentional barcode, which iPhones and Android phones can read and interpret. The phone reads the QR code and displays whatever media is hidden behind that QR code (on the internet).
It’s about as useful in customer-grade applications as warts are on pigs, and is the new ‘fab’ to sweep across the world. It’s a marvelous thing in factory-grade applications, however.