System for determining a distortion model for an optically distorting medium, the system including an image sensor located at an image acquisition position behind the optically distorting medium, and an image processor coupled with the image sensor, the image sensor acquiring an obstructed image of an object located substantially at infinity, when the optically distorting medium is located between the image sensor and the object in a line of sight connecting the image sensor and the object, the image sensor acquiring an unobstructed image of the object, when the optically distorting medium is absent from the line of sight, the image processor receiving information respective of the obstructed image and the unobstructed image from the image sensor, the image processor identifying a plurality of features in the unobstructed image, and a respective feature in the obstructed image for each of the identified features in the unobstructed image, thereby determining pairs of associated features, the image processor determining a distortion parameter for each of the pairs of associated features, the image processor determining a reference distortion model for the optically distorting medium, respective of the image acquisition position, according to the distortion parameters.