This contribution presents application of digital correlation method for optical measurement of displacements and techniques for improvement of data processing. The main point of the paper is a comparison of two different techniques of the data processing of the same experiment. First one is based on determination of the displacement field using the image of studied body surface at the beginning and at the end of load application, while the second evaluation technique relies on sequential evaluation and addition of the partial displacement fields derived from comparison of adjacent image pairs in the sequence. It is shown that the later approach is favorable from the point of view of the total error of the experimental results. This observation is especially true in the case of large deformations as explained in the final discussion of the paper. The scripts performing calculation were written in MATLAB providing a suitable development environment thanks its powerful image processing and data presentation functions.