1. A storage medium comprising a security feature, comprising a substrate ( 1 , 4 , 10 ), at least one functional layer ( 2 , 5 , 11 ), at least one first feature written in the at least one functional layer ( 2 , 5 , 11 ) which is observable in reflection, at least one second feature written in the at least one functional layer ( 2 , 5 , 11 ) which is observable in transmission, and wherein at least the one first feature is individualized and wherein the at least one second feature has a diffractive structure.