A novel real-time approach to achieve optical image processing to evaluate the difference between the two images is carried out by implementing a phase reversal concept in Twyman-Green interferometer. The phase reversal is accomplished by varying the pressure within an air-filled quartz cell inserted in one of the arms of the interferometer. Initially, the interferometer is aligned to obtain broad interference fringes in the cell region. Then the input imageries are introduced in both the arms of the interferometer and adjusted for exact registration as seen in the plane of observation. By introducing the phase change of π-radians between the two arms of the interferometer, the difference between the two input images is detected in real-time. Phase shift calibration and image subtraction carried out by the proposed method is presented with the experimental results.