The moments constitute a well-known tool for image analysis and recognition tasks. The family of moments that has the most advantages is the discrete orthogonal moments. A set of these moments is the Hahn moments, as they have a great number of advantages in comparison with other sets of moments. The main disadvantage of moments, including Hahn moments, is the high computational cost, which is increased as higher order moments are involved in the computations, so the real-time analysis is hard to be done. We propose an effective approach for the computation of Hahn moments. The gray image is decomposed in a set of binary images that are named as bitplanes. The most significant bitplanes are represented using image block representation and their moments are computed fast using block techniques. The least significant binary images are substituted by a constant ideal image called “half-intensity” image, which has known Hahn moment values. The proposed method has low computational error, low computational complexity, and under certain conditions is able to achieve real-time processing rates.