Ferroelectric materials are of great interest because of their rich applications. Several techniques have been used to understand their behaviors. Two-beam coupling configuration using LiNbO₃ crystal as a recording mediums has been extensively used for real-time in-plane displacement of a transparent rough object. Low-power He–Ne laser was used to create the index grating of the speckle pattern inside the crystal and to read the grating to give the Young’s fringes. In this technique, for the in-plane displacement measurement, the image of the transmitted object is formed in the crystal. The aim of our work is to extend the applicability of the two-beam coupling configuration using LiNbO₃ as a recording medium for the evaluation of in-plane displacement of a transparent rough object using speckle photography method; measurement uncertainty of in-plane displacement was studied on a wide range of displacements using experimental and new theoretical formula for displacement measurement.