In an in-person setting, using smartphones to sharemultimedia is hindered by their small display size. Furthermore, multimedia sharing applications, such as social media, are not designed for exclusive in-person interactivity, leading to a lack of simple methods for doing this action in the presence of friends or other collaborators. Besides sharing, there is a lack of options for in-person multimedia organization, which is an increasingly important aspect of collaborative multimedia-focused workflows, such as social media marketing and design thinking. We propose a platform that uses Mobile Augmented Reality (MAR) to support collaborative multimedia sharing and organization. MAR provides the possibility of viewing and interacting with virtual elements in physical space. We explored various types of interactions that enjoy the unique characteristics of the medium to encourage effective collaboration, and, from these, we developed an interaction taxonomy. This interaction taxonomy provides categories for the different types of interaction that should be included in an application designed for this context, such as sharing and multimedia spatial manipulation. Furthermore, we implemented and evaluated a multimodal photocentric application composed of interactions derived from the taxonomy. We found that the interaction set derived from the taxonomy allowed users to, collaboratively, achieve complex organization goals and that its implementation was adequate at supporting it.