  Clarifying conditions for the existence of a gravitational picture for a
given quantum field theory (QFT) is one of the fundamental problems in the
AdS/CFT correspondence. We propose a direct way to demonstrate the existence of
the dual black holes: imaging an Einstein ring. We consider a response function
of the thermal QFT on a two-dimensional sphere under a time-periodic localized
source. The dual gravity picture, if it exists, is a black hole in an
asymptotic global AdS$_4$ and a bulk probe field with a localized source on the
AdS boundary. The response function corresponds to the asymptotic data of the
bulk field propagating in the black hole spacetime. We find a formula that
converts the response function to the image of the dual black hole: The view of
the sky of the AdS bulk from a point on the boundary. Using the formula, we
demonstrate that, for a thermal state dual to the Schwarzschild-AdS$_4$
spacetime, the Einstein ring is constructed from the response function. The
evaluated Einstein radius is found to be determined by the total energy of the
dual QFT. Our theoretical proposal opens a door to gravitational phenomena on
strongly correlated materials.

High Energy Physics - Theory;General Relativity and Quantum Cosmology