Different theories have been proposed on the mechanisms that control the latent image formation and the image formation upon thermal development of photothermographic materials based on silver halide and silver carboxylates. The purpose of this study is to get closer to reaching a general consensus on the actual mechanisms involved. Evidence is provided which calls the concept of an epitaxial interface between silver halide and silver carboxylate into question, as well as its photochemical reactivity. Instead an alternative mechanism for latent image formation is proposed. Tribromomethyl-substituted compounds are present in all commercial materials as antifoggants or printout stabilizers. In this study, an important role in the mechanism of thermal development is attributed to these tribromomethyl-substituted compounds. An arrested development study was conducted using TEM. The results of all these investigations led to a novel theory for the mechanisms of underlying image formation in photothermographic materials.