  In a recent work on rotating black hole shadows [Phys. Rev. D{\bf 101},
084029 (2020)], we proposed a new approach for calculating size and shape of
the shadows in terms of astrometrical observables with respect to
finite-distance observers. In this paper, we introduce a distortion parameter
for the shadow shapes and discuss the appearance of the shadows of static
spherical black holes and Kerr black holes in a uniform framework. We show that
the shape of the shadow of a spherical black hole is circular in the view of
arbitrary observers, and the size of the shadows tends to be shrunk in the view
of a moving observer. The diameter of the shadows is contracted even in the
direction perpendicular to the observers' motion. This seems not to be
understood as length contraction effect in special relativity. The shape of
Kerr black holes is dependent on motional status of observers located at finite
distance. In spite of this, it is found that there is not a surrounding
observer who could view the shape of the Kerr black hole shadows as
circularity. These results could be helpful for observation of the Sagittarius
A* in the centre of the Milky Way, as our solar system is moving around the
centre black hole.
