create a 3d file for 3d printing from a photo

There is a stool whose shape has to be slightly altered and a 3d file needs to be created so that it can be 3d printed . The shape of the base of the stool need to be like an inverted trumpet . The final size of the table will have a top dia of 700 mm bottom dia of 500 mm and an overall height of 760 mm . The model 3d structure may needs to proportional and could be as little as 6 inches tall .