  Upcoming Event Horizon Telescope (EHT) observations will provide a unique
opportunity to reveal the innermost region of the radiative inefficient
accretion flow (RIAF) around the Galactic black hole, Sgr A*. Depending on the
flow dynamics and accumulated magnetic flux, the innermost region of an RIAF
could have a quasi-spherical or disk-like geometry. Here we present a
phenomenological model to investigate the characteristics of the black hole
shadow images with different flow geometries, together with the effect of black
hole spin and flow dynamics. The resulting image consists in general of two
major components: a crescent, which may surround the funnel region of the black
hole or the black hole itself, and a photon ring, which may be partially
luminous and overlapped with the crescent component. Compared to a
quasi-spherical flow case, a disk-like flow in the vicinity of a black hole
exhibits the following image features: (i) due to less material near the funnel
region, the crescent structure has a smaller size, and (ii) due to the
combination of emission from the flow beside and behind the black hole, the
crescent structure has a more irregular shape, and a less smooth brightness
distribution. How these features can result in different observables for EHT
observations is discussed.
