In　this　paper,　a　novel　image-based　visual　servoing　(IBVS)　approach　based　on　a　second-order　image　dynamics　model　is　proposed　to　realize　the　positioning　of　unmanned　aerial　vehicles　(UAVs)　under　disturbances.　Specifically,　the　mathematical　relationship　between　the　image　motion　and　the　UAV　accelerations　is　described　by　a　second-order　image　dynamics　model,　which　decouples　the　image　motions　and　the　UAV　dynamics.　Based　on　this　model,　a　sliding-mode　observer　is　implemented　to　estimate　the　external　disturbances.　Then,　the　output　of　the　observer　is　exploited　in　the　dynamic　IBVS　controller　designed.　As　a　result,　the　proposed　dynamic　IBVS　controller　can　be　applied　in　environments　under　uncertain　disturbances　without　position　and　translational　velocity　measurements.　The　Lyapunov　analysis　is　provided　demonstrating　the　global　asymptotic　stability　of　the　proposed　dynamic　IBVS　controller　and　the　exponential　convergence　of　the　image　errors.　Finally,　a　visual　positioning　experiment　is　implemented　to　verify　the　feasibility　and　effectiveness　of　the　proposed　IBVS　method.