The computational cost of embedding information in a digital representation is reduced by making a set of at least two copies of the digital representation and altering subdivisions of the copies so that corresponding subdivisions in the copies are distinguishable from each other. The subdivisions may...http://www.google.co.uk/patents/US7555650?utm_source=gb-gplus-sharePatent US7555650 - Techniques for reducing the computational cost of embedding information in digital representations
