| CPC G09F 3/0294 (2013.01) [G06K 19/06159 (2013.01); G06K 19/06037 (2013.01); G09F 2003/0257 (2013.01)] | 19 Claims |

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1. A label structure for tagging a product item, the label structure comprising:
a first graphic pattern having a first number (N1) of pixels and printed on a first portion of said label structure, wherein the first graphic pattern by itself does not form an optical code readable by an optical decoding device;
a second graphic pattern having a second number (N2) of pixels and printed on a second portion of said label structure, said second graphic pattern forming the optical code readable by the optical decoding device; and
a shielding means capable of hiding or making visible said first graphic pattern depending on values taken by a physical quantity to which said label structure is exposed;
wherein said first and second graphic patterns can be observed in combination, when said first graphic pattern is made visible by said shielding means;
wherein the combination of said first and second graphic patterns forms an optical code readable by the optical decoding device, when said first graphic pattern is made visible by said shielding means;
wherein the combination of the first graphic pattern and the second graphic pattern is indistinguishable from the second graphic pattern when being read by the optical decoding device.
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