  Camera fingerprints based on sensor PhotoResponse Non-Uniformity (PRNU) have
gained broad popularity in forensic applications due to their ability to
univocally identify the camera that captured a certain image. This fingerprint
of a given sensor is extracted through some estimation method that requires a
few images known to be taken with such sensor. In this paper, we show that the
fingerprints extracted in this way leak a considerable amount of information
from those images used in the estimation, thus constituting a potential threat
to privacy. We propose to quantify the leakage via two measures: one based on
the Mutual Information, and another based on the output of a membership
inference test. Experiments with practical fingerprint estimators on a
real-world image dataset confirm the validity of our measures and highlight the
seriousness of the leakage and the importance of implementing techniques to
mitigate it. Some of these techniques are presented and briefly discussed.
