  In this paper, we first consider null geodesics of a class of charged,
spherical and asymptotically flat hairy black holes in an
Einstein-Maxwell-scalar theory with a non-minimal coupling for the scalar and
electromagnetic fields. Remarkably, we show that there are two unstable
circular orbits for a photon in a certain parameter regime, corresponding to
two unstable photon spheres of different sizes outside the event horizon. To
illustrate the optical appearance of photon spheres, we then consider a simple
spherical model of optically thin accretion on the hairy black hole, and obtain
the accretion image seen by a distant observer. In the single photon sphere
case, only one bright ring appears in the image, and is identified as the edge
of the black hole shadow. Whereas in the case with two photon spheres, there
can be two concentric bright rings of different radii in the image, and the
smaller one serves as the boundary of the shadow, whose radius goes to zero at
the critical charge.
