  We show theoretically that the multi-photon states obtained by cloning
single-photon qubits via stimulated emission can be distinguished with the
naked human eye with high efficiency and fidelity. Focusing on the
"micro-macro" situation realized in a recent experiment [F. De Martini, F.
Sciarrino, and C. Vitelli, Phys. Rev. Lett. 100, 253601 (2008)], where one
photon from an original entangled pair is detected directly, whereas the other
one is greatly amplified, we show that performing a Bell experiment with
human-eye detectors for the amplified photon appears realistic, even when
losses are taken into account. The great robustness of these results under
photon loss leads to an apparent paradox, which we resolve by noting that the
Bell violation proves the existence of entanglement before the amplification
process. However, we also prove that there is genuine micro-macro entanglement
even for high loss.
