If your photos were taken on plain background you may align photos with even more accuracy. Any background colour is good as far as there is a contrast between person and backcloth.
By default the horizontal centre point of the image located between person eyes. If person turned their head and looking aside both eyes can be visually off centre. In this situation you may use geometrical centre of the head.
If you cropping whole figure and want it to be in the middle of the photo you may select centre by body position. This will place in centre even figures that are turned or standing in not symmetrical poses.
Another useful option is “Find Head Top over Background”. That way you may guarantee that tops of all heads on all photos will be on the same level. It is very helpful when for of people in series have high hair-do.
Click on preset icons below the image to see how it works: