A set of digital imaging methods derived from the Voronoï diagram is proposed and tested on various liquid–granular flow applications. The methods include a novel pattern-based particle-tracking algorithm, as well as estimators of the three-dimensional granular concentration from two-dimensional images. The proposed algorithms are able to resolve individual grain motions even for rapid shear flows involving dense, fluctuating granular ensembles. Full automation is achieved, allowing the derivation of accurate statistics from large sets of individual measurements, as well as the construction of complete sets of grain trajectories. Results are presented for different applications: homogeneous fluidization, steady uniform debris flow, and unsteady debris surges.