A fluorescing structure (made of one or several molecules) can be considered as an ideal point source of light for use in a near-field optical microscope [Michaelis , Nature 405, 325 (2000)]. This paper discusses how the image-object relationship is made easier to understand by introducing the concept of photon local density of states (LDOS). Specifically, we show that the LDOS determined by Green's dyadic calculations provide the relevant interpretation of the images recorded with a single fluorescing molecule as source of light. Recent experimental results are analyzed on this basis.