The paper presents a surface flatness control system designed for installation on a production line. Such a system allows the control of all blanks leaving the production line in terms of measuring flatness made in the conditions prevailing on the production line. The article discusses 3D imaging methods enabling the construction of a surface image. An analysis of imaging parameters for each method is presented. For the selected imaging method, an analysis of the imaging resolution is presented. An example of flatness measurement for a selected element after a welding operation is shown. The flatness measurement algorithm is discussed, and the results of measurements are presented. The results of measurements for selected two product groups are presented.