Detector systems

A detection system comprising a plurality of magnetic field generators and a plurality of magnetic field detectors located adjacent to a detection area, and a control system arranged to generate magnetic field using the generators, and, for each of the generators, to make measurements of the magnetic field generated using each of the detectors, a processor arranged to process the measurements to generate a plurality of sets of data characterizing the detection area as an object moves through the detection area and to combine the sets of data to form a resultant data set, wherein said resultant data set is representative of a planar image, and a displacement sensor arranged to detect a displacement of a part of the object away from a reference position, wherein the processor is arranged to correct for the displacement when combining the sets of data and wherein said correction shifts a detected feature back to the reference position.