The kinematics characteristics of the human knee joint can be represented by its centrodes. This paper provides a method, called the photograph method, to construct the centrodes by using commercial digital camera to take the sequential pictures. In order to eliminate the undesired movements, a testing chair and a brace are specially designed. Two types of curve fitting methods are introduced to smooth the measured data. The differential method is applied to construct the centrodes of knee joints from the measured data. This paper provides a safe way to measure the centrodes of human knee joints.