Careful and precise are not the standards for
copyright protection.
Creative is. In the case of an image which is completely from a
single public domain source, there just isn't anything creative being
done. You stitch together the tiles in a completely algorithmic
manner. If anyone holds the copyright on the resulting work, it would
be the person who chose what scene to picture (the user of the
software), not the person who wrote the software. That is also the
person who put the work in fixed form, another requirement for
copyright protection.
I say show me the creativity. I don't see it. I actually don't see
much creativity in any satellite photography, but when it comes to
creativity from Google in a typical Google Earth shot, I don't see any
at all.
The algorithm would be creative, which should be enough. Would you say
a painting made using a rubber stamp wasn't creative because anyone
can cover stamps in paint and put them on a piece of paper? The
creativity comes in making the stamp, and so, what you make with that
stamp is copyrightable.