An image analysis technique has been developed in order to determine the drop size distributions of sprays produced by low-velocity plain cylindrical jets. The particle sizing method is based on incoherent backlight images. Each drop is analyzed individually in the image. The two-dimensional image resulting from the projection of the three-dimensional object shape (the drop) on a screen (the video sensor surface) is modeled. The model, based on the point spread function formulation, has been developed to derive a relation between contrast and relative width of individual drops. This relation is used to extend the domain of validity of drop size in terms of size range, out of focus and image resolution. The shape parameter is determined for each drop image through morphological analysis. Spherical and non-spherical droplets are then sorted on the basis of this parameter. Non-spherical drops are regarded as non-fully atomized liquid bulks or coalesced drops. Finally, the droplet size distribution of true spherical droplets is established for a low-velocity plain cylindrical liquid jet.