In this study, we propose a quantitative diabetic neuropathy diagnostic method which uses the foot sole images based on skin hardness of patients. The purpose of this study is to estimate the severity of the diabetic neuropathy based on the foot plantar image. We compared the evaluation between the method of the change of the foot plantar image and classical, neurological, and hemodynamic assessments. A positive correlation (0.517) was presented between the proposed evaluation and the classical assessments. Also, we compared the area change rate with the hardness of the foot plantar measured by durometer and the hardness based on proposed image diagnosis. A significant positive correlation was found between the area change rate and the hardness of big toe (0.300), first metatarsal head (0.448), and heel (0.400). A significant positive correlation (0.468) was also found between severity and skin hardness in the heel.