Thanks Steven, this is quite helpful. I like the approach of using webcam images, will definitely check out the Lifeslice project.
Right now I'm using Facebook photos since many people have photos of themselves over time on this single platform.
The analysis right now is manual, but I plan to automate using Python / machine vision. The hope is to derive a number of health insights from facial images - mood, stress levels, body fat % / BMI, etc. - as an overall means of passive health tracking, but also as a tangible emotional motivator (self-visualization has a powerful effect).
Doing some initial work on making this into a product here: http://www.enfluence.io/ , feel free to sign up here for updates, will also let folks know when we have something more production ready to use.
Below are some more materials for reference, where I specifically looked at BMI
Originally posted at http://quantifiedself.com/2014/10/shawn-dimantha-face-health/
Video of talk can be seen here: http://vimeo.com/108722655
Slides from talk here: http://www.slideshare.net/shawndimantha/20140924-quantified-self-presentation-using-facebook-for-health-insights