The culture of tattooing pigs has a history of several millennia. Pigs have long been tattooed to keep an eye on them as they grow and are transported for sale. Even ancient farm manuals on the tattoo process have survived.
In addition, pigskin is very similar in quality to human skin and tattoo artists have traditionally trained on it before starting to stuff anything on a person. Pigskin can easily be bought at the butcher's markets. And even the top-notch tattooists today continue to train on pigskin and teach others how to do it.
A live pig, however, became a tattoo and art object not so long ago. Today, a domestic tattooed pig is no longer surprising - as, indeed, any tattooed animals - from bald cats to tattooed fish.