One thing you could try is the magnet selection tool in the Select tab. This tool tries to make a selection outline that lines up with edges in a photo. Once you have the person's face selected, copy with Ctrl+C and paste into the other photo with Ctrl+V.
The magnet tool might not work super well on large images though, so you may also want to try the polygon, free form, or wand selection tools too.
Note: to add to an existing selection, hold shift and make a selection. To remove areas from an existing selection, hold alt while making a selection.