Image resolution and signal level in fluorescence microscopy through inhomogeneous turbid media consisting of scatterers of multiple sizes under single- (1p), two- (2p), and three-photon (3p) excitation have been investigated based on a modified Monte Carlo model. The effects of the size distribution and the concentration distribution of scattering particles are explored. Simulation results reveal that the size and the concentration distribution both have an impact on image formation in media consisting of small particles and that 3p excitation has the most significant impact. In media with scatterers of a large size, both size and concentration distributions lead to a slight effect. Image formation in a mixed medium containing small and large scattering particles is more affected by the large particles.