You can add a texture where you paint all your tattoo’s in with texture painting into the model’s UV’s. That way all your tattoo’s live inside one texture instead of having a lot of small texture files plugged all over the place.
You have to add them one by one if you want that fine detailing of where they are. Or you could export your UV layout and in a imaging application just place them following your UV’s. That is cumbersome though. Also, you can as well have say a texture that contains five tattoo’s and paint them into the model on a bulk like that. But one by one is the way to go if you want to place them exactly where you want on the model.
