We consider estimation of the limiting detection ranges for single objects (in absence of background) and discrimination of such objects against the background surface when they are observed with a help of passive or active optoelectronic systems through scattering and absorbing media. We propose analytical equations, applicable at any optical depth of the medium under conditions of weakly developed scattering processes (small scattering coefficients). The analysis of these equations has shown that the use of optical illumination does not guarantee an increase in limiting detection ranges for objects observed through turbid media.