Optical transfer function (OTF) of the turbulent atmosphere and telescopic receiving optical system are considered theoretically using different methods of postdetector processing of images of incoherently illuminated objects observed through the turbulent atmosphere. When approximating the transmission function of a receiving lens by a Gaussian shape simple analytical expressions are obtained for OTFs of the turbulent atmosphere and a telescope. The following image processing methods are examined: the averaged image recording ("very long" averaging times) and short-exposure images ("very short" averaging times), namely, Labeyrie and Knox–Thompson methods and the method of triple correlation of the image intensity. Potentialities and applicability limits of the methods under different conditions of optical radiation propagation through the turbulent atmosphere are discussed. The influence of the finiteness of the inner scale of turbulence on the OTFs under consideration is also estimated.