The practice of tattooing people has existed since around 6000 B.C as a form of expression and to mark group affiliation. Whether you call them 'ink,' 'tats,' or 'skin art,' tattoos are body modifications that involve inserting ink underneath the epidermis. To understand how this is done, the video below captures the process in slow motion.
Amazing Video Of Tattooing Close Up, In Slow Motion

Tattoo by beast love via Flickr. Licensed by CC.