M is the mass of the hole in units where G = c = 1: for a hole of one solar mass, 1 M is about 1.48 km. The camera hovers in place, held there by a rocket.
What you are looking at
The black disc is the shadow. Every ray aimed inside it falls into the hole. It is 2.6 times wider than the event horizon: light passing closer than √27 M ≈ 5.2 M is captured.
The arc over the top and under the bottom is the far side of the disk, behind the hole. Its light is bent over and under the shadow towards you.
The thin bright ring hugging the shadow is light that went once or more around the hole before it escaped.
Stars near the shadow are stretched into arcs and seen twice: the hole is a lens. Switch on the sky grid to see the lensing.