Depth can also be thought of as distance. This third dimension tells the eye how much space exists between an object that is close to the viewer, and an object that is further away. It is this dimension that gives 3D animated characters their “rounded” look. 3D art uses lighting and shading, shadows and blur to create the life-like effect. Shadows haven’t been used in tattoo designs for long; it’s only been in the last few decades that tattoo artist have taken tattoos into this third dimension.
To create a 3D effect, tattoo artists need to add highlights to the design. These are areas of “high light” or shine. Shading is used to create a rounded effect, and shadows are added to add depth and distance to the tattoo design. This is how 3D tattoos can look like they are inside the body, part of the body or sitting on top of the skin.
3-D tattoos don’t necessarily need to be photorealistic. As long as they have convincing lighting, shading and shadows, a 3D tattoo can be a cartoon or fantasy character. This 3D effect can even be used in artistic tattoos, to give a sketched design the appearance of being shaded with a pencil, or a painted tattoo design the effect of shadows being added with a paint brush.
Here are a great collection of 3D Tattoos