  We analytically calculate the correlation potential of a test ion near a
\emph{strongly} charged plate inside a dilute $m:-n$ electrolyte. We do this by
calculating the electrostatic Green's function in the presence of a nonlinear
background potential, the latter having been obtained using the nonlinear
Poisson-Boltzmann theory. We consider the general case where the dielectric
constants of the plate and the electrolyte are distinct. The following generic
results emerge from our analyses: (1) If the distance to the plate $\Delta z$
is much larger than a Gouy-Chapman length, the plate surface will behave
effectively as an infinitely charged surface, and the dielectric constant of
the plate effectively plays no role. (2) If $\Delta z$ is larger than a
Gouy-Chapman length but shorter than a Debye length, the correlation potential
can be interpreted in terms of an image charge that is three times larger than
the source charge. This behavior is independent of the valences of the ions.
(3) The Green's function vanishes inside the plate if the surface charge
density is infinitely large; hence the electrostatic potential is constant
there. In this respect, a strongly charged plate behaves like a conductor
plate. (4) If $\Delta z$ is smaller than a Gouy-Chapman length, the correlation
potential is dominated by the conventional image charge due to the dielectric
discontinuity at the interface. (5) If $\Delta z$ is larger than a Debye
length, the leading order behavior of the correlation potential will depend on
the valences of the ions in the electrolyte. Furthermore, inside an
\emph{asymmetric} electrolyte, the correlation potential is \emph{singly}
screened, i.e., it undergoes exponential decay with a decay width equal to the
Debye length.
