The design of an image based measurement system for the online inspection of electromechanical parts is described. A two-camera architecture is introduced in order to highlight all the required details involved in the measurements. The design takes into account both the interfacing and the real-time issues that assure an effective online operation. The description of the measurement system and the corresponding installation on the production line points out a methodological approach to the design of these kinds of measurement systems. The paper provides details about the algorithms for the localization and the measurement of the required quantities, as well as the calibration procedure and the error correction. Experimental tests for the performance evaluation are presented and discussed in terms of timing and accuracy.