A finite-difference frequency-domain method combined with digital image processing is used to analyze real photonic crystal fibers. To overcome the difficulties imposed by the irregularity of the fiber cross section, the fiber structure is first obtained from the scanning electron microscopy (SEM) image of a real photonic crystal fiber by such digital image processing techniques as thresholding segmentation and Wiener filtering. Image interpolation and window filtering method are then employed to realize mesh division and permittivity averaging. Parameters obtained above are used in fiber property analysis by the finite-difference frequency-domain method. It is shown that the proposed method gets accurate fiber dispersion compared with measurement, and also that the calculated mode field distributions correspond well with those recorded in the experiment.