Described embodiments include a system and a method. A conversion table correlates each digit of the conversion table base system to a respective machine recognizable feature in an ultrasound echo response by a respective micro-object of a set at least two ultrasound-differentiable micro-objects (hereafter “set of micro-objects). An encoding apparatus encodes a data set into machine recognizable features of at least two micro-objects of the set of micro-objects pursuant to the conversion table. A selector apparatus picks from a physical set of the micro-objects at least two micro-objects having the machine recognizable features corresponding to the encoded data set. Each micro-object of the physical set of micro-objects is biocompatible and suitable for implantation in a vertebrate subject. Each micro-object while implanted returns an ultrasound echo having a machine recognizable feature differentiating the micro-object over each other micro-object of the set of micro-objects.
