論文アブストラクト：Items in social media such as photos may be co-owned by multiple users, i.e., the sharing decisions of the ones who upload them have the potential to harm the privacy of the others. Previous works uncovered coping strategies by co-owners to manage their privacy, but mainly focused on general practices and experiences. We establish an empirical base for the prevalence, context and severity of privacy conflicts over co-owned photos. To this aim, a parallel survey of pre-screened 496 uploaders and 537 co-owners collected occurrences and type of conflicts over co-owned photos, and any actions taken towards resolving them. We uncover nuances and complexities not known before, including co-ownership types, and divergences in the assessment of photo audiences. We also find that an all-or-nothing approach seems to dominate conflict resolution, even when parties actually interact and talk about the conflict. Finally, we derive key insights for designing systems to mitigate these divergences and facilitate consensus.