Droplet shape measurement using image based techniques can be conducted using shape parameters which consist of a number of geometric features of a droplet image. The accuracy of calculating these shape parameters and their capability in revealing shape deviation is considerably affected by the discretization of the image with a camera CCD. In this paper, a simulation of digital images is conducted to investigate the error caused by image discretization. The effect of this error on calculating area, perimeter, and also a selected number of shape parameters are investigated. Digital images of circular and elliptical discs at different image/pixel size ratio and locations relative to the pixel grid have been generated to simulate the projected view. Results show that the shape parameters demonstrate different levels of sensitivity to the desirable factor of shape deviation and the undesirable factor of image discretization. A "clearance factor" has been suggested and used to rank the shape parameters based on their compensation between sensitivity to shape deviation and image discretization.