We present a new practical scheme to study the spectroscopic properties of molecules embedded in optically complex surroundings. The response function accounting for the modification of the spectroscopic behavior of the molecules is derived self-consistently in direct space through the numerical solution of Dyson's equation. We apply this scheme to investigate near-field optical effects due to fluorescence phenomena. Experimentally relevant examples show that the dramatic decay of the molecular lifetime upon approaching a surface defect could achieve well-resolved imaging of subwavelength structures.