Time-resolved photoelectron imaging of negative ions is employed to study the dynamics along the reaction coordinate in the photodissociation of IBr(-). The results are discussed in a side-by-side comparison with the dissociation of I(2) (-), examined under similar experimental conditions. The I(2) (-) anion, extensively studied in the past, is used as a reference system for interpreting the IBr(-) results. The data provide rigorous dynamical tests of the anion electronic potentials. The evolution of the energetics revealed in the time-resolved (780 nm pump, 390 nm probe) I(2) (-) and IBr(-) photoelectron images is compared to the predictions of classical trajectory calculations, with the time-resolved photoelectron spectra modeled assuming a variety of neutral states accessed in the photodetachment. In light of good overall agreement of the experimental data with the theoretical predictions, the results are used to construct an experimental image of the IBr(-) dissociation potential as a function of the reaction coordinate.