A novel technique and an instrument for on-line, quantitative imaging diagnostics and process control in thermal spraying have been developed and tested in laboratory and industrial conditions. In-flight spray particles are imaged by their natural luminosity with a short-exposure, digital CCD camera system. Particle images are processed using digital image processing techniques in a PC computer. The number of particles per frame and the spatially resolved particle velocities are calculated from the images. Spectrally resolved image information is further used to determine pyrometric two-color particle temperature. A number of different modes of data presentation have been developed. The developed instrument can be used to determine particle number, velocity and temperature distributions of individual in-flight particles from the imaged region of interest of the plume. Dividing the imaged area into smaller sections, spatial distributions of these parameters can be studied. SprayWatch system provides a technically simple, easy to operate, single imaging instrument, which can provide a visual overview of the spray plume in combination with quantitative evaluation of the most important spray particle parameters. In this paper examples of using the monitoring system with plasma and HVOF spraying are presented. Preliminary test results of using a semiconductor laser generated light sheet to detect cold particles is also demonstrated.