Black holes, unlike many astronomical objects, were first predicted theoretically as a direct consequence of Einstein's General Theory of Relativity. They were initially thought unphysical, even by Einstein himself. The Event Horizon Telescope (EHT), a Very-Long-Baseline Interferometry (VLBI) experiment that links together multiple radio telescopes around the globe, captured the first event horizon scale resolution black hole images in 2019. It provided a new test of general relativity in strong gravity regime. In this talk, I will start by giving an overview of theory and observation methods black holes. I will then describe the mathematics used in reconstructing black hole images and discuss some open questions.
