The image is about a merger of two black holes, before the actual merger takes place.
The two largest of the dark regions are slightly distorted images of two the black holes. Distortion is due to light being bended asymmetrically by the combined gravity of the two black holes.
The two smaller dark areas show the respective other black hole in a strongly distorted version, since the light - or missing light - of the other black hole is bended around the respective less distorted appearing black hole by about 180 degrees, somewhat similar to an arrangement of uneven mirrors.
You may interprete the phenomenon of the smaller dark areas as an extreme version of Einstein rings.