1. A signal-processing device which processes transparent images each expressed by transparent superimposition of a target and a background different from the target, the device comprising: a transparent image acquiring unit that acquires the transparent images each including the target at a plurality of times; a calculating unit that calculates a component of the transparent image originating from the target and a component of the transparent image originating from the background at a given time t among the plurality of times in association with estimated values of at least one of a distribution originating from the target and a distribution originating from the background at the plurality of times and that evaluates consistency with the transparent images at the plurality of times; and an updating unit that updates the estimated values of at least one of a distribution originating from the target and a distribution originating from the background at the time t based on the evaluation result of the calculating unit.