Assessing posture and measuring different angles, such as the Q-angle in the lower limbs, are important findings for clinical examination and the planning of therapeutic interventions. An increased Q-angle has been considered a risk factor for many disorders and injuries. Photogrammetry is a widely used non-invasive technique for measuring aspects of posture. However, the application of this technique depends on the measurement procedure, the training of the assessor, and the image processing tool used. This study aimed to investigate the reliability of the photogrammetry technique in the evaluation of the lower limb for Q-angle using the Leonardo analysis system. Fifty-nine participants (aged 18–35) were recruited from the University of Patras. An assessment of test-retest and inter-rater reliability was conducted. The procedure included photography and static analysis on the Leonardo PL800 postural analysis system and evaluation of the Q angle by photogrammetry. Reliability was tested using the intraclass correlation coefficient (ICC) to examine the degree of correlation of values between the two measurements, the first completion and the repetitive completion, and between the measurements of the two evaluators of the instrument. Excellent test-retest reliability is recorded for the Q angle on the right lower limb and good test-retest reliability for the left limb; moderate inter-rater reliability among technical photogrammetry researchers through the Leonardo posture analysis system is shown for the evaluation of the Q angle of both lower limbs. Further studies are needed to investigate the system’s reliability at other body sites.