  A detailed analysis is presented of gravitational microlensing by intervening
compact objects of the black hole shadows imaged by the Event Horizon Telescope
(EHT). We show how the center, size, and shape of the shadow depend on the
Einstein angle relative to the true/unlensed shadow size, and how the location
of the lens affects the shift, size, and asymmetry of the black hole shadow due
to microlensing. Assuming a supermassive black hole (SMBH) casts a
circular-shaped true shadow, microlensing can create an asymmetry of up to
approximately 8\%, which is twice the asymmetry caused by the SMBH's spin and
its tilt relative to us. Furthermore, the size can be enhanced by $\sim$50\% of
the true shadow. Currently, the terrestrial baselines of EHT lack the
resolution to detect microlensing signatures in the shadows. However, future
expansions of EHT, including space-based baselines at the Moon and L$_2$, could
potentially enable the detection of microlensing events. For Sgr A$^*$, an
event rate of 0.0014 per year makes the microlensing phenomena difficult to
observe even with space-based baselines for the stellar population in the
stellar bulge and stellar disk for lens masses $\sim M_\odot$. Nonetheless, the
presence of a cluster of 20,000 stellar-mass black holes in the central parsec
of the Milky Way, expected to arise from dynamical friction acting on infalling
stellar clusters, significantly boosts the event rate. Hence, continuously
monitoring the shadow of Sgr A$^*$ could offer novel insights into the compact
object population surrounding the Galactic Center.
