Something else that always must be considered, along with everything else already mentioned, is if anyone is not standing straight or if they are bending a knee somewhat. This you can not see in these pictures.
Actually measuring a persons height, via the top of their heads, for basketball purposes is rather academic. The length of necks and the size of a persons head are variable. Look at the level of their shoulders and consider the length of their arms. Reach is all important, since it is very unusual for anyone to either shoot or block shots with the top of their heads.