The phenomena of Damage localization, which characterized as the rock mass suddenly enter into the deformation localization stage after a period of uniform deformation, is the beginning of rock failure. Damage localization is also the precursor of rock failure. Utilizing the image enhancement and segmentation technology, the rule of damage evolution of limestone under triaxial compression is analyzed. Moreover, The computerized tomography images are analyzed by the method of digital image processing, which includes threshold partition and edge detection, and then the relationship between computerized tomography image and damage evolution is discussed. Meanwhile, the dependence of fractal dimensions of rock section on the axial stress is determined by the method of box-counting dimension. It is concluded that the fractal dimension may reach a minimum value at the point of damage localization, and after that damage become more severe.