The quality of imaging systems is usually expressed using the modulation transfer function (MTF). MTF is also used to express the quality of transmitted images through a random medium. The resolution, as well as MTF, is essentially dependent on the properties of such media. Transmitted images are often affected by the presence of particulate matter (aerosol, dust, fog) and turbulence between object and receiver. It is usually assumed that the turbulent field is of the Kolmogorov type and, in imaging systems, the long- and short-exposure MTF characterization is based on this type of turbulence. However, experimental data indicates that the turbulence can be different from Kolmogorov's case. Influence of Kolmogorov and non-Kolmogorov turbulence statistics on imaging system performance is analyzed for different propagation scenarios, and the generalized MTF is presented.