We give a broad discussion of existing typical works devoted to particle image processing. We propose the approach based on the postprocessing of coherent images of the particles at various planes of the volume. These images can be obtained both by reconstruction of inline digital hologram and by means of defocussing of the lens with high numerical aperture. Processing of the reconstructed holograms or recorded images is carried out using the proposed image analysis approach based on the edge-point linking and thresholding technique, which is considered to be simple to implement and reliable. After the review of existing methods and approaches, we noted that, in general, only cases of low concentrations are considered and, therefore, we investigated the performance of our proposed approach for characterization of particles of high density in a volume of optical medium. In this study of the method, we increase the concentration of particles until we ensure that every volume element comprises many particle images, yet these images do not create a speckle pattern, and look for the concentrations at which normalized density distributions of the particles can be constructed with an acceptable error for us. It is shown that the proposed approach exhibits good results of recognition and allows investigation of high concentrations.