Photodynamic therapies combining the action of a photosensitizer (PS), molecular oxygen, and light make it possible to destroy certain infectious sites and tumors. The incorporation of photosensitizers in nanocarriers allows for better control of their distribution in tissues and increases their concentration in the area that will be then illuminated. Nanoemulsions of glyceryl trioctanoate (GTO) have been designed in which pyropheophobide a (Pyro-A) or its lipid conjugate (Pyro-Lipid) are both stabilizing and photostimulable agents. In this work, we studied by surface pressure measurements and Brewster angle microscopy (BAM) analysis the organization of the interfacial films of nanodroplets. Comparison of preformed porphyrin nanoemulsions and two porphyrin-GTO mixtures, one mimicking the composition of the nanoemulsions and the other that of a porphyrin-rich interfacial film, highlighted the role of GTO and porphyrin derivatives in the formation, organization, and elasticity of the interfacial films in nanoemulsions. Pyro-Lipid and GTO can mix, and some of the GTO molecules remain inserted in the interfacial film at high surface pressures. In contrast, Pyro-A and GTO do not mix well and tend to segregate, leaving Pyro-A alone in the condensed interfacial film. The results of this study demonstrate the importance of characterizing the interfacial properties of porphyrin derivatives and their interaction with the oil to design stable nanoemulsions with well-controlled optical properties.