The present disclosure describes a method for controlling a wet processing system includes dispensing one or more chemicals into a processing chamber according to one or more process parameters. The method also includes injecting one or more illumination markers into the processing chamber and obtaining images representing locations of the one or more illumination markers. The method further includes determining a trajectory of an illumination marker of the one or more illumination markers based on the images and determining whether the determined trajectory is outside a predetermined trajectory range. In response to the determined trajectory being outside the predetermined trajectory range, the method further includes adjusting the one or more process parameters.