A method of recognizing changes in a detection zone is provided in which three-dimensional image data of the detection zone are detected and evaluated to recognize changes with reference to three-dimensional reference image data. The detection zone is divided into cells in this process. Reference limit values at which heights objects are recognized are determined in a teaching phase. In an operating phase, a maximum value and/or a minimal value of the heights of currently recognized objects is/are determined from the respective detected image data and a change is recognized on a deviation with respect to the reference limit values.