1. An identification system for identifying documents bearing a magnetic stripe recorded with digital data and having a repeatable magnetic characteristic, comprising: a magnetic stripe sensor for sensing the magnetic field of the magnetic stripe to provide an analog signal representative of said recorded digital data and said repeatable magnetic characteristic; a detector for defining sampling intervals in said analog signal; a circuit for defining a target number of samples in said sampling intervals; a digitizer for sampling said analog signal in accordance with said samples defined in said sampling intervals to provide a target-number of digitized samples representative of said repeatable characteristic; a selection processor for selecting a predetermined number of said digitized samples from said target number of digitized samples; and a storage for storing at least one of said predetermined number of said digitized samples as an identifier for said document.