A manufactured item includes an outer part including at least one outer material; and an identifier including at least one three-dimensional configuration corresponding to the identifier, the at least one three-dimensional configuration being embedded within the outer part. The three-dimensional configuration includes at least one of (1) a substantially empty cavity in the at least one outer material, and (2) at least one identifying material filling at least part of a cavity in the at least one outer material. Where at least one identifying material fills at least part of a cavity in the at least one outer material, the at least one outer material is substantially opaque to visible light. The item may be manufactured using one of the processes generally known as rapid prototyping, but other manufacturing processes may be used as well. Methods for making the item and for making a computer-readable representation of the item are also disclosed.