1. An image-based structural health monitoring system, comprising: a marker image acquisition unit configured to acquire marker images of markers attached onto a surface of a structure; a marker coordinate calculation unit configured to calculate coordinates of the markers in the marker images; a shape function determination unit configured to determine a shape function by performing spline interpolation based on the calculated marker coordinates; and a structural health evaluation unit configured to evaluate structural health of the structure by calculating strain or stress of the structure based on a radius of curvature calculated at each location on the determined shape function.