Melanin is one of the most important pigments in human skin.Estimating melanin distribution is required in many different research fields such as anthropology,dermatology and cosmetics.The current noninvasive estimation methods are mostly based on spectroscopy,which may not be available in many applications.In this paper,a fast estimation algorithm is proposed.Based on the principles of optics and skin biophysics,the process of the skin colour formation is inversed and modeled by an Elman network,and the corresponding melanin distribution can be obtained.The algorithm was evaluated on many skin images with different camera models and illumination conditions.Experimental results demonstrate that the proposed algorithm performs significantly better than other estimation methods.It can help researchers easily detect skin regions with abnormal amount of melanin pigment.