And in the coming years astronomers hope to image a black hole directly (in radio wavelengths). The few closest supermassive black holes (in center of galaxies) have their event horizon angular diameters just big enough to be resolved by VLBI (very-long-baseline interferometry). See [3] for details and a simulated image.
I believe this is supposed to happen this year, last I heard was this summer but they haven't finished the analysis yet. The data was collected back in April, petabytes of harddrives flown to a central processing location.
[1] https://en.wikipedia.org/wiki/Event_Horizon_Telescope
[2] https://eventhorizontelescope.org/
[3] Seeing Black Holes: from the Computer to the Telescope (https://arxiv.org/pdf/1804.03909.pdf)