A processing system for an input device includes a sensor module and a determination module. The sensor module includes sensor circuitry coupled to transmitter electrodes and receiver electrodes. The sensor module is configured to transmit transmitter signals with the transmitter electrode and receive resulting signals with the receiver electrodes. The determination module is configured to obtain a set of measurements for an input object detected in a sensing region of the input device from a capacitive image, and perform, based on the set of measurements, a multistage classification to obtain a classification result identifying a type of the input object. wherein the capacitive image is generated based on the resulting signals.