A method of decoding a machine-readable optical code that includes a first code including a plurality of first elements formed on or in a substrate, the first code specifying first information, wherein one or more of the first elements includes a second code on or in the substrate, the second code including a plurality of second elements specifying second information; and wherein the first code and the second code are machine-readable optical codes, the method comprising: using a first image reader to record the first code, the first code specifying first information to form a first recorded image; using a processor to decode the first information from the first recorded image; using a second image reader to record the second code to form a second recorded image; and using the processor to decode the second information from the second recorded image whereby the machine-readable optical code is decoded.