  The optical properties of rotating black holes in Kaluza-Klein theory
described by the total mass, spin, and electric and magnetic charges are
investigated in detail. Using a developed general relativistic ray-tracing code
to calculate the motion of photons, the numerous shadows of Kaluza-Klein black
holes are generated. The properties of the black hole shadow and the light
deflection angle around these black holes are also studied in order to put
constraints on the parameters of Kaluza-Klein black holes using M87* shadow
observations. The possibility of imposing constraints on Kaluza-Klein black
holes using shadow observations is investigated. Moreover, we find that small
charges (electric and magnetic) of the black hole can meet these constraints.
We conclude that with the current precision of the M87* black hole shadow image
observation by the EHT collaboration, the shadow observations of Kaluza-Klein
black holes are indistinguishable from that of the Kerr black hole. Much better
observational accuracy than the current capabilities of the EHT collaboration
are required in order to place verified constraints on the parameters of
modified theories of gravity in the strong field regime.
