Cervical spondylosis has gradually become a high-incidence disease in today's society. The cervical range of motion (CROM) is widely used as the evaluation criterion of cervical status, whereas the existing methods of CROM measuring are not humanized enough. Consequently, the purpose of this study was to develop a novel photogrammetric method to assess three-dimensional CROM. Three smartphone cameras were controlled to simultaneously capture three-direction photographs of the subject wearing the special designed device with three mark lines. The obtained photographs were uploaded to a PC and the mark lines in each photograph were extracted by utilizing both the Radon transform and the Hough transform. By calculating and combining the tilt angles of three mark lines, the CROM of the subject was indirectly determined. The performance of our method was compared with the goniometer-based method: the inter-instrument reliability was excellent for all six cervical movements with intraclass correlation coefficients 0.99; the degree of agreement between the two methods was high with Pearson's coefficients 0.98; and the Bland-Altman plots also revealed the validity of our method. Moreover, the concept of a cervical motion curve was put forward to describe the movement track of the neck in order to reflect the cervical health status. The proposed approach is feasible, automatic and convenient for the measurement of CROM and the generated cervical motion curve can intuitively exhibit the trajectory of the neck. This technique that can easily acquire the biomedical information of the cervical spine has tremendous potential in the diagnosis, healthcare and wellness management of the neck.