  We study the optical appearance and the apparent radiation flux of a thin
accretion disk around the static Janis-Newman-Winicour naked singularity. We
confine ourselves to the astrophysically most relevant case, when the solution
possesses a photon sphere, assuming that the radiation emitted by the disk is
described by the Novikov-Thorne model. The observable images resemble closely
the visual appearance of the Schwarzschild black hole, as only quantitative
differences are present. For the Janis-Newman-Winicour solution the accretion
disk appears smaller, and its emission is characterized by a higher peak of the
radiation flux. In addition, the most significant part of the radiation is
concentrated in a closer neighbourhood of the flux maximum. The results are
obtained independently by two alternative methods, consisting of a
semi-analytical scheme using the spherical symmetry of the spacetime, and a
fully numerical ray-tracing procedure valid for any stationary and axisymmetric
spacetime.
