Image prior a simple and an effective method is proposed in this paper –for a single input image dark channel prior method is applied to remove fog. To remove fog from the out-door environmental images this dark channel prior plays an important role. While considering the out-door environmental images it is observed that in the image there will be equal intensive levels with one channel having lowest intensity. By this method to find fog using dark channel prior we can estimate the thickness of fog and get fog free image. Considering the results on more number of outdoor images it can be stated that dark channel prior is most suitable method to get better quality image in foggy environment.