How can we use a touch sensor to detect a specific object like a biometric fingerprint sensor?
You probably can’t is the simple answer. Your body acts as an antenna and via capacitance your touch can be detected electronically. Apart from the actual weight,glass or cup does not provide the same signal. If the cup was metal, you could use an inductive technique to detect it. But it could not determine if it were a cup or a badge. A vision system would be the obvious solution methinks.