Multi-frequency techniques are widely adopted for eddy current testing. One of the advantages of these techniques can be deduced from the skin depth formula (formula available in paper) where delta is the standard depth of penetration at excitation frequency f, with the other two parameters, mu and sigma, related to material properties. Thus, an inspection can be performed at several depths into the material with the simultaneous use of multiple frequencies. To investigate the potential of a multi-frequency eddy current technique (MFECT) for corrosion quantification, an experiment was carried out on a two-layered fuselage lap joint splice. Two data fusion approaches, namely Bayesian inference and multiresolution analysis, are investigated in this study to fuse eddy current images of different frequencies. The corrosion types are classified based on the percentage of material loss. The estimated thickness results, based on the fusion processes, are compared with accurate thickness maps obtained from teardown X-ray inspection data.