The study of the distribution of droplets formed due to underside dropwise condensation provides information about the heat transfer by the droplets. To find the count and size distribution of droplets the image processing technique is proposed so that the whole process could be automated. Moreover, more accurate results can be obtained as compared to manual tracing and theoretical droplet growth model simulation. The watershed transformation for effective segmentation of the droplet image, prior to finding the size distribution was used. The proposed method has been applied to scanning electron microscopy (SEM) images of droplets formed on condensed bismuth metal vapor on stainless steel substrate and graphite substrate.