The black hole shown in the first published black-hole image in 2019 was M87*.
M87* is the supermassive black hole at the centre of Messier 87, a giant elliptical galaxy about 55 million light-years from Earth. The Event Horizon Telescope, a planet-sized network of radio observatories, produced the image by combining observations through very-long-baseline interferometry.
The famous image shows a bright, asymmetric ring surrounding a dark central region. The dark area is the black hole’s shadow, not a photograph of the event horizon as a physical surface. The ring is produced by radiation from hot plasma near the black hole, while gravity bends the light around it.
M87* has a mass of about 6.5 billion Suns. Its enormous scale made it a practical first target despite its great distance. The galaxy also contains a spectacular relativistic jet extending thousands of light-years, powered by processes in the black hole’s surrounding environment.