  Images from the vicinity of the black hole horizon at the Galactic centre
(Sgr A*) could be obtained in the near future with a Very Large Baseline Array
of sub-millimetre telescopes. The recently observed short-term infrared and
X-ray variability of the emission from Sgr A* implies that the accretion flow
near the black hole is clumpy or unsteady. We calculate the appearance of a
compact emission region (bright spot) in a circular orbit around a spinning
black hole as a function of orbital radius and orientation. We find that the
mass and spin of the black hole can be extracted from their generic signatures
on the spot image as well as on the lightcurves of its observed flux and
polarisation. The strong-field distortion remains noticeable even when the spot
image is smoothed over the expected ~20 microarcsecond resolution of future
sub-millimetre observations.
