We propose a noncontact method for measuring structural deformation using off-axis digital image correlation. An efficient and high-precision algorithm that is insensitive to the accuracy of the initial guess is proposed and validated through numerical simulation. Image displacements in pixels are converted to physical displacements in millimeters using a calibration model based on a new method of measuring the objective distance. A new image-based structural deformation measurement system is proposed and validated using laboratory test results. The proposed method is easy to implement and accurate for structural deformation measurements.