NASA resources on Cygnus X-1
Images of Cygnus X-1 From NASA Archives
The above image was taken by the optical Schmidt telescope at the Palomar Observatory and shows the area of sky occupied by the black hole Cygnus X-1 and its companion HDE 226868. Distant background stars show up as isolated bright (yellow or white) pixels.
The difference in intensity seen in these pixels is due to fluctuations in the background.