A data storage device is provided in which encoded binary machine-readable, digital hierarchical data may be stored. The data is represented by X-nary characters in a matrix. Two different hierarchical 2-D barcodes may be superimposed to increase the data storage capacity. The device is integrated in...http://www.google.co.uk/patents/US20030116630?utm_source=gb-gplus-sharePatent US20030116630 - Encrypted biometric encoded security documents
