1. A bridge structural safety monitoring system, comprising: an imaging optical system module arranged for capturing an image of at least one monitoring area of a bridge to create a standard image under a normal operation condition of the bridge, and continuously capturing images of the monitoring area to obtain a plurality of monitoring images; an image correlation computing module arranged for comparing the standard image with the plurality of monitoring images to obtain a plurality of displacement correlation coefficients of the monitoring area of the bridge; and a central console arranged for receiving each displacement correlation coefficient, and determining a using condition of the bridge according to each displacement correlation coefficient; wherein the imaging optical system module further comprises an electric power module for receiving a utility power to supply an electric power required by the imaging optical system module; and wherein the electric power module comprises: an energy storage unit arranged for receiving a utility power, storing the electric power into the energy storage unit, and supplying the electric power to the imaging optical system module if the energy storage unit has not received the utility power; and a power management unit arranged for evaluating whether or not the energy storage unit has received the utility power, and controlling the energy storage unit to store the electric power or supply the electric power.