Dangerously high heat loads, electromechanical stresses and runaway electron (RE) currents can occur during a tokamak disruption (global magnetohydrodynamic instabilities during which plasma confinement is suddenly lost). A reliable disruption mitigation strategy is therefore required for ensuring safe tokamak operation and preventing such outcomes. The current ITER design envisages to mitigate disruptions and RE beams via shattered pellet injection, a concept which has been extensively studied in DIII-D and is currently being tested on JET. The SPI effectiveness relies on deep penetration of shards into the plasma, which in JET, can be analysed by identifying and following their ablation plumes observed on the fast visible camera videos. A particle tracker has been under development for two years and has been applied to study SPI videos of the recent JET experimental campaign. Particle tracking is obtained by merging multiple general-purpose open-source and commercial image feature identification and matching algorithms via a weighting scheme for increasing overall solution robustness. Considering RE avoidance experiments, first qualitative results show the existence of a correlation between deep SPI penetration (shards reaching the lower-high field side wall) and RE beam currents lower than 100kA. Videos from RE suppression experiments suggest improved penetration of light impurities into RE beams compared to heavier ones. The complete assessment of this observation is ongoing through detailed analyses of the complex images resulting from RE beam – SPI shard interactions.