  Can the observation of the "shadow" allow us to distinguish a black hole from
a more exotic compact object? We study the motion of photons in a class of
vacuum static axially-symmetric space-times that is continuously linked to the
Schwarzschild metric through the value of one parameter that can be interpreted
as a measure of the deformation of the source. We investigate the lensing
effect and shadow produced by the source with the aim of comparing the expected
image with the shadow of a Schwarzschild black hole. In the context of
astrophysical black holes we found that it may not be possible to distinguish
an exotic source with small deformation parameter from a black hole. However,
as the deformation increases noticeable effects arise. Therefore, the future
more precise measurement of the shadow of astrophysical black hole candidates
would in principle allow to put constraints on the deviation of the object from
spherical symmetry.
