Qualifying ringdown and shadow of black holes under general parametrized metrics with photon orbits Song Li, Ahmadjon A. Abdujabbarov and Wen-Biao Han Eur. Phys. J. C, 81 7 (2021) 649 Published online: 23 July 2021 DOI: 10.1140/epjc/s10052-021-09445-6