This purpose of this investigation is to develop a new method for obtaining pore-size distribution (PSD) and other pore parameters from inner structure images. This method can be summarized into four key procedures to realize its functionality. A MATLAB program was composed to make the method applicable for image analysis. Image tests on wastewater biofouling layer samples showed the validity and feasibility of the method for analyzing intrinsic porous structures. The structural information obtained by this method can facilitate the understanding of transport phenomena, e.g., water flow and species diffusion inside porous structures.