The structural health monitoring of ferromagnetic materials is essential for controlling product quality. This paper presents the first known characterisation, utilising magnetic induction spectroscopy, of the magnetic permeability of ferromagnetic materials, a property that can facilitate such monitoring. Magnetic induction coils are interrogated by a sweep of excitation frequencies in the range of 1-100 kHz, with amplitudes of induced voltages collected from both non-magnetic and ferromagnetic specimens, and their associated spectral permeability imaged. The reconstructed images show that magnetic permeability can be reconstructed using frequency difference imaging in the investigated frequency range. As such, the relative magnetic permeability of a ferromagnetic specimen can be reconstructed without needing a time difference measurement. This provides a robust imaging approach for the material characterisation of ferromagnetic specimens.