I've seen some black hole images and I've seen some movies about it e.g(interstellar). I wonder why it has a light around it. Even if I know that light can't escape through it. Can someone enlighten me about this? Thanks.
Well, you're partially correct here. A black hole traps everything inside its event horizon. Outside of the event horizon, matter (and energy) can still escape from its gravitational pull. This is due to the fact that the escape velocity of a black hole beyond its event horizon becomes greater than the speed of light itself.
So, the light you see around a black hole is actually just the matter and energy that is outside the event horizon. In other words, you're seeing the light and matter that is not actually inside the black hole. This "stuff" usually orbits the black hole at large fractions of the speed of light.