The chemistry of a thermally developed photographic system based on silver carboxylate is investigated both in the model system and in the film sample. The reaction path is found to consist of the disintegration of the silver carboxylate crystal structure under thermal development (step 1), the formation of silver ion carriers which can diffuse in the molten media (step 2), and the reduction reactions of silver ion to metallic silver by the reducing agent (step 3). In the first reaction step, XRD patterns and FT–IR spectra show that phthalic acid receives silver ion from crystalline silver behenate and becomes di-silver-phthalate. In the second reaction step, the complexes of phthalazine and silver ion are identified as the silver ion carriers in molten media by ¹³C–NMR, density functional calculations of ¹³C–NMR chemical shift, and TOF–SIMS. The diffusion coefficients of silver ion carriers are measured by pulsed field gradient ¹H–NMR at the development temperature. In the final step, the reduction of silver ion by the bisphenol-type reducing agent is analyzed by the identification of the reaction products. It is found that this reducing agent has eight equivalent reducing power. An overall reaction mechanism for thermally developed photographic systems based on silver carboxylate is proposed.