A crane control system for determining a suitable real-time operating regime for a crane arranged to lift cargo from a marine vessel, the system includes an imaging means associated with the crane, a processing means, and a memory means. The imaging means is arranged to capture images of the vessel when it is located generally below the crane and within the operational range of the crane. The processing means is operable to calculate from the captured images movement parameters characterizing the movement of the vessel relative to the crane. The memory contains performance data representative of the performance characteristics of the crane and cargo data representative of the weight of individual items of said cargo. The processing means is further configured to compare the calculated movement parameters to the performance data and the cargo data and to determine from said comparison a safe operating regime for the crane.