This work focuses on an innovative Eddy Current Imager dedicated to the high-speed and high-resolution non-destructive testing of large metallic structures, such as the riveted lap joints of aircrafts. The system produces time-harmonic in – phase and in – quadrature eddy current images, thanks to a specific linear magneto-optic set-up, which actually provides a true measurement of the 2-D spatial distribution of the magnetic flux density at the surface of the inspected structure. In view of quantitative imaging of defects in planar structures, an appropriate numerical model, based on an efficient integral formulation, is presented and validated against the measurements.