How to Understand the Black Hole Image

We have just seen the first image of a black hole, the supermassive black hole in the galaxy M87 with a mass 6.5 billion times that of our sun. But what is that image really showing us? This is an awesome paper on the topic by J.P. Luminet: Image of a spherical black hole with thin accretion disk Astronomy and Astrophysics, vol. 75, no. 1-2, May 1979, p. 228-235 Using my every day intuition I wondered: will we see the “shadow“ of the black hole even if we’re looking edge on at the accretion disk? The answer is yes because the black hole warps space-time, so even if we wouldn’t normally be able to see the back of the accretion disk, we can in this case because its light is bent up and over the black hole. Similarly we can see light from the bottom of the back of the accretion disk because it’s bent under the bottom of the black hole. Plus there are additional images from light that does a half turn around the black hole leading to the inner rings. What about the black hole “shadow“ i