The surface of the eye is always covered with water, and if he/she opens his/her eyes, the temperature gradually falls because of the evaporation of water. The transition of the temperature differs whether he/she wears contact lenses or not, and furthermore, there exists some differences between soft and hard lenses. Basing on these properties, this paper proposes a system to extract and distinguish contact lenses by using a thermo-vision camera. Some experimental results show about 72% success and this means the possibility to apply this basic method to the preprocessing of biometrics.