Just throwing this out there off the top of my head. Something along these lines....
5pts for an archery kill (recurve, compound, xbow, etc.)
3pts for a gun kill (shotgun, rifle, muzzloader, etc.)
1pt for each legal point
1pt for each inch of spread (either inside or outside, and picture must show ruler)
Few examples:
8 pointer with a 15" spread shot with a compound = 28 points. 10 pointer with a 15" spread shot with a rifle = 28 points. 6 pointer with a 17" spread shot with an Xbow = 28 points.