Plot and extract real movement dimension of a moving object

Hi everyone, I'm considering the recording of the opening and closing of the mouth with a tablet. If I place a sphere marker (known dimensions) on person's lips, how can I plot and extract the real movement in terms of dimension of the marker during the opening and closing? I have the intrinsics parameters of the tablet camera and i'm on a known distance from the person.

Thanks in advance

Answer 1

[Image Analyst]

See my attached tracking demo.

[Nicolas Emiliani]

Thank you for your answer but this is not very helpful to me