In the paper, features of optoelectronic systems design for measuring geometrical parameters of objects are examined. In particular, diameter measurement systems based on digital cameras are studied. A comparative analysis of telecentric systems and parallel light beam systems is performed, and advantages and disadvantages of these measuring systems are compared. Further attention is focused on the less costly and more simple telecentric systems. The impact of object longitudinal displacements on measurement accuracy of object diameter for such system is investigated. Consequently, a scheme for evaluation and compensation of objects longitudinal displacements based on linear laser pointers is proposed. Also, an image processing algorithm to remove the specified error of object small movements in the work area is elaborated. The source of systematic error of the proposed scheme related to object observation from a single point is discovered, and additional algorithm for removing this error is developed. Additionally, a working formula for diameter actual value calculation is obtained. The working formulas listed in the paper can be useful to developers of modern optoelectronic instrumentation.