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The Johannsen black hole (BH) is a generic rotating BH admitting threeconstants of motions (energy, angular momentum, and Carter constant) and ischaracterized by four deviation parameters besides mass and spin, which couldbe a model-independent probe of the no-hair theorem. We systematically studythe dynamics of null particles around Johannsen BH, revealing the effects ofthe deviation parameters on the BH shadow as well as the effects of spin. Byusing the shadow boundaries of M87* and SgrA*, for the first time, thedeviation parameters of those BHs are constrained. The detailed results dependon the spin $a$ and inclination angle $ \theta_0$. Assuming $a=0.2$ and$\theta_0=15^{\circ}$, the deviation parameter $\alpha_{13}$ are constainedwithin $\sim $ [-3.5, 6] for M87* observation and [-3, 0.5] for SgrA*observation. We also show the images of a Johannsen BH surrounded by aPage-Thorne thin accretion disk observed by a remote observer with aray-tracing method and discuss the effects of the deviation parameters ondeforming the accretion disk image, which could be tested by observations withhigher sensitivities in the future.

Dynamics of null particles and shadow for general rotating black hole