The dynamics of structures with joints commonly show nonlinearity in their responses. This nonlinear behavior can arise from the local dynamics of the contact interfaces. The nonlinear mechanisms at an interface are complicated to study due to the lack of observability within the contact interface itself. In this work, digital image correlation (DIC) is used in combination with a high-speed camera to observe the local motion at the edge of the interface of a bolted lap joint. Results demonstrate that it is possible to use this technique to monitor the localized motion of an interface successfully. It is observed that the two beam parts of the studied lap joint separate when undergoing bending vibrations and that there is a clear asymmetry in the response of the left and the right end of the interface. Profilometry indicates that the asymmetry in the response is due to the mesoscale topography of the contact interface, highlighting the importance of accounting for surface features in order to model the nonlinearities of a contact interface accurately.