A bstractWe present a detailed analysis of the calibration procedure to be performed in order to extract from magneto-optical images the local values of magnetic induction and electric current density on a plane over and inside the superconducting sample respectively. The interaction between the spontaneous magnetization of the indicator ®lm and the full magnetic ®eld distribution in the specimen region has been considered. In particular, the generally disregarded interaction of the indicator ®lm with in-plane magnetic ®elds, that is with the component parallel to the indicator surface, is retained in the model. The current density distribution is obtained by the numerical inversion of the Biot±Savart law. In order to incorporate the in-plane ®eld e ect into the inversion scheme, we have constructed an iterative procedure which successfully takes into account the full magnetic induction ®eld. A set of experimental data on a high-temperature superconducting YBa2Cu3O7¡x ®lm is presented to show the actual impact of the new analysis method, for what concerns both the local values of the magnetic induction and the electrical current density evaluation.