The important point of MPI is the analysis of leakage field in the defective regions. The analysis of leakage field depends on many factors such like geometry and character of defect. In general the calculation of magnetic leakage fields arising from such defects presents an extremely complicated mathematical problem and is practically insoluable, since the inhomogeneities have complex geometrical shapes and may differ in physical nature. Therefore, this paper describes Hall probe measurements of residual leakage field around artificial flaws in alloy steel bar, and shows how the results to recent developments in 2D dipole and analytic models of the magnetic field defect interaction.