Scale was a major problem. The father had the largest hand but no photo showed me how the rest related to that size. I had to take reference photos of side by side father/young son, father/twin son, mother/father, grandmother/mother, and twin/twin. These could have been, that is, should have been much more accurate and controlled for consistency. The snapshots provided visual cues for rough estimates of the size of each hand relative to the others.
See wholeo.net for a few photos related to this project.