  New physics beyond General Relativity can modify image features of black
holes and horizonless spacetimes and increase the separation between photon
rings. This motivates us to explore synthetic images consisting of two thin
rings. Our synthetic images are parameterized by the separation as well as the
relative flux density of the two rings. We perform fits to the visibility
amplitude and analyze closure quantities. The current Event Horizon Telescope
array cannot detect the presence of a second ring in the region of parameters
motivated by particular new-physics cases. We show that this can be improved in
three ways: first, if the array is upgraded with Earth-based telescopes with
sufficiently high sensitivity, second, if the array is upgraded with a
space-based station and third, if super-resolution techniques are used for the
data obtained by the array.
