The biggest challenge in 3D CG is to fake actual surface details.
It is a requirement to balance out render time and manageable mesh density.
In the recent years high res mesh sculpting became a very hot topic in CG
is is now being adapted into many other areas such as Product and Jewelry design.
The process is as following.
The reason for that is because the image is applied to a second low polygon model the render result
will be as desired, but without having to deal, work, animate with a high polygon model.
There are two ways to generate those images:
Realtime Displacement Texture
Texture based displacement is using the subsurf subdivision modifier and than a displacement modifier.
As you can see the right mesh is the subdivided result of the Base Mesh with the displacement added.Normal Mapping Texture
Texture based normal mapping is a much more advanced version of bump mapping.