  Black holes in General Relativity are described by space-time metrics that
are simpler in comparison to non-vacuum compact objects. However, given the
universality of the gravitational pull, it is expected that dark matter
accumulates around astrophysical black holes, which can have an impact in the
overall gravitational field, especially at galactic centers, and induce
non-negligible effects in their observational imprints. In this work we study
the optical appearance of a spherically symmetric black hole both when orbited
by isotropically emitting light sources and when surrounded by a (geometrically
and optically thin) accretion disk, while immersed in a dark matter halo. The
black hole geometry plus the dark matter halo come as a solution of Einstein's
field equations coupled to an anisotropic fluid whose density component follows
a Hermquist-type distribution. Even in situations in which the geodesic
description differs profoundly from the isolated black hole case, we find minor
modifications to the primary and secondary tracks of the isotropic orbiting
sources, and to the width, location, and relative luminosity of the
corresponding photon rings as compared to the Schwarzschild black hole at equal
black hole mass and emission models. This fact troubles distinguishing between
both geometries using present observations of very-long baseline
interferometry.
