I make an overhead of the photo or scan it into a computer if it is a good side profile. I then project it on a wall and move the projector closer or further from the wall until the full length photo matches a known measurement on the rifle. I use butt height, trigger pull length, barrel length, etc. If there are no known measurements I usually use a trigger pull length of 13 1/2. I tape poster board to the wall and trace the profile marking the breech, trigger. etc. It may look grainey depending upon the quality of the photo, but I can get a rough profile to use to build the rifle. It works for me, but I am sure other folks have a better way.
Roger Sells