The resolution of the photos is vitally important, and on mobile phones there is always the problem of anamorphosis (distortion). I prefer photos in a portrait format, so as to have a maximum of detail.
For instance, holiday snaps, or someone laughing, make lovely souvenirs, but are terribly difficult to exploit. The eyes should be wide-open, not submerged by a wide-open mouth, and the best angle is a 3/4 frontal view.
We make the choice of photo together. Once the portrait is finished, I scan it and send you the scan for you to validate it. The photo chosen is used as the basic model. Once I have started work on it, it is no longer possible to change for another photo.