re: Incredible clarity
Along with the difficulty of tracking, which probably is computer controlled, is focusing.
As ISS tracks across the sky its elevation is always changing thus going out of focus, so I imagine a lot of team work went into when to snap the shutter for the photo to come in so clear.
There are focusing software out there for stars and other objects, but I don’t know if they would operate the same on a moving target forever changing its distance from a terrestrial based platform.