1. A method for determining posture-related information of a subject using the subject's image, the method comprising: receiving a first image of a subject in a first posture; determining, from the first image, first positions of a first pair of joints; determining, from the first positions, a first body segment length of a first body segment associated with the first pair of joints; receiving a second image of the subject in a second posture; determining, from the second image, second positions of a second pair of joints; determining, from the second positions, a second body segment length of a second body segment associated with the second pair of joints; determining, based on a relationship between the first and second body segment lengths, whether the first and second pairs of joints correspond to a pair of joints of the subject; If the first and second pairs of joints are determined to correspond to a pair of joints of the subject, determining, based on the second positions, information of a posture of the subject; and providing an indication regarding the information of a posture of the subject.