  Employing 3D GRMHD simulation, we study the images of a geometrically thin
jet, whose emissions concentrate on its surface, for accretion system
surrounding a central spinning BH. By introducing a strong magnetic field, we
observe three phases of BH accretion evolution: (a) initially, both the
accretion rate and the magnetic flux on the horizon gradually increase; (b) at
an intermediate stage, the magnetic flux approximately reaches saturation, and
a jet forms via the Blandford-Znajek (BZ) mechanism; (c) ultimately, the entire
system achieves a dynamic equilibrium, and a magnetically arrested disk (MAD)
forms. We carefully study the jet images during the saturation and MAD regimes
at various frequencies and from different observational angles. We reveal the
presence of U-shaped brighter lines near the jet surface boundaries, which can
be attributed to the photons whose trajectories skim over the jet surface. The
existence of these brighter lines is a unique feature of a geometrically thin
jet. Moreover, we notice that the jet images are relatively insensitive to the
observed frequencies of interest. Additionally, we observe that the
time-averaged images for the highly oscillating MAD regime show only slight
differences from those of the saturation regime.
