What is the light source in the black hole images?
The radiation being detected in this case is mostly synchroton radiation, caused by energetic electrons spiralling around magnetic field line, rather than thermal radiation, but it comes from the same place (the disk). The actual evidence for light bending is, I believe the dark area in the middle, which is several times larger than the actual event horizon and is caused because the light that would have been coming to us from that direction has been bent away.