Why are there no stars in the background when photos are taken from space of earth?
ISS photos show only sunlit surface of Earth. As ISS is quite near Earth, there is no exposed background. Earth hides space behind. So, stars behind are hidden by Earth..
When Earth hides Sun to ISS during its nights, the astronauts therein will see only night hemisphere of Earth. . .
That is correct A. S. Adikesavan, but I don't think that is what he/she meant.
I believe that this person meant pictures farther away from the Earth. not just pictures from the ISS.
In that case, the answer is simple.
The light Earth is reflecting into the camera is greater than the light of the stars in the background.
Imagine you were looking at your cellphone with the sunlight in the background, you wouldn't be able to see as well as if it would've been in the shadow.