Methods, systems, and programming for user identification and authentication are presented. In one example, an apparatus for user authentication is disclosed. The apparatus comprises: a surface on which an object is placed; a light source configured for providing light illuminating a first portion of the surface; a brightness measuring unit configured for measuring brightness distribution in a second portion of the surface, wherein the brightness distribution is caused by the object that spreads the light from the first portion to the second portion; and a determiner configured for determining whether the object is an organic body part based on the brightness distribution.