Phase-shifting interferometry provides a fast and accurate mean of computing the geometric moments of an image irradiance distribution. The technique is based on a mathematical relationship between the moments and image Fourier transform. The optical system includes a Mach-Zehnder interferometer and a Fourier transforming lens to generate the irradiance spectrum of the interferogram. Its sampling is achieved with a CCD detector arrays. A digital processor interfaced to an image processing system is used to compute the moments of the input function. The accuracy of the method is discussed, and the experimental results are shown.