In order to do a great hair simulation, please follow this guide.
Keep 60-80 CM distance and have a horizontal view of your whole head.
Have a top picture taken or make sure your whole scalp is visible.
Make a horizontal picture of your right side.
Make a horizontal picture of your right side.
Have a picture taken of the backside or use a bathroom mirror.
Upload a picture of when you had full hair. Preferely close up.