Bulk properties of transparent and dilute water in paraffin oil emulsions stabilized with sodium dodecyl sulfate (SDS) are analyzed by optical scanning tomography. Each scanning shot of the considered emulsions has a precision of 1 mu m. The influence of aluminum oxide nanoparticles in the structure of the water droplets is investigated. Depending on concentrations of SDS and nanoparticles, a transition occurs in their shape that changes from spherical to polymorphous. This transition is controlled by the SDS/alumina nanoparticles mixing ratio and is described using an identification procedure of the topology of the gray level contours extracted from each images. The transition occurs for a critical mixing ratio of R-crit approximate to 0.05 which does not significantly depend on temperature and electrolyte concentration. This structural change seems to be a general feature when emulsifying dispersions and most probably involves both interfacial and bulk phenomena.