One of my recent freelance projects was a tattoo design through Guru. The client had a unique request for an elephant tattoo design for his shoulder that was able to look solid and 3-dimensional from a distance without using any shading. We agreed that building up line work to create the illusion of depth would be the best solution, going for an old rubber stamp look.
Took a photo of the tattoo area and super-imposed the elephant shape. This helped us make decisions about positioning and how much the elephant should be rearing up and reaching towards the neck.
Original stance sketch
Concept changed to a standing elephant, checked placement and level of detail with a work-in-progress temporary tattoo print-out
Photoshop composite elephant from over a dozen references, and final elephant with all line work. This ended up being even more detail than was needed, so it was simplified for the tattoo artist before the final transfer.