Every camera shows a face a little differently depending on how far away it is, and no single distance is the real one. For progress photos, use the same distance every time and your photos compare like with like.
Where does the "selfies make your nose 30% bigger" figure come from?
A 2018 paper in JAMA Facial Plastic Surgery (Ward et al.). The researchers built a mathematical model of an average face and compared a photo taken from about 30 cm with one taken from 1.5 m, a common portrait distance. In their model, the base of the nose came out about 30% wider at 30 cm. It was a model built from average measurements, with no photos of real people tested.
Is a photo from 1.5 m more accurate than a selfie?
Each distance shows a face differently, and 1.5 m is a photography convention. Vision scientists replied in the same journal that how a face looks in a photo also depends on how the photo is viewed, including how far the screen is from your eyes (Cooper and Banks). Two photos at different distances aren't a fair comparison of each other. Neither one is wrong.
Does it matter for progress photos?
Only if the distance changes between photos. Two photos taken at the same distance show your face the same way, so you're comparing like with like. That's the job B&A does: it measures your distance and only takes the photo when you're back where you were last time.
What distance should I take progress photos from?
One you can repeat. Arm's length is the distance most people can get back to on their own, and the B&A camera guide holds you to it so every photo lines up with the last.
