How dangerous are latent prints on the sensor?
In test reports about fingerprint sensor devices occasionally is criticized that residuals of the fingerprint of an authorized person remaining on the sensor might be activated by an attacker to gain unauthorized access (e.g., by breathing on the sensor). This effect indeed can be demonstrated with a couple of sensor types (e.g., capacitive and optical surface sensors). However, this effect requires the sensor to be clean or cleansed (which is often not even notified by the testers!). Touching the sensor surface several times degrades the quality of the latent prints in such a way that a false acceptance becomes very unlikely. Since in practice a cleaning of the sensor is hardly ever necessary, latent prints on a sensor are a much smaller risk than generally supposed. The remaining risk might be further reduced by software, if fingerprints are refused whose position coincide too much with the last positively verified fingerprint.
