Magneto-optical (MO) imaging using an MO material is one of the most important imaging techniques for measuring magnetic field distributions. The technique is attracting attention because of its ability to visualize magnetic fields and current distributions at a wide range of temperatures from cryogenic to room temperature or higher, a wide range of length scales from micrometers to several tens of centimeters, and a wide range of frequencies from DC to GHz. Nevertheless, further development of films with good MO properties is required in order to extend the range of applications of MO imaging. In this paper, developments related to bismuth-substituted iron garnet films, R3−xBixFe5−yGayO12 (R = Y, Nd; 1 ≤ x ≤ 3), prepared by metal–organic decomposition for MO imaging plates are reviewed. In addition, an MO imaging plate with an electroluminescent backlight, which enables wide-area MO imaging, and the MO color imaging technique, which indicates the strength of a magnetic field using colors, are reviewed.