How far away must one be to photograph earth?

Answer 1

You can do it standing in your own back yard. Simply stand there and point the camera straight down at the ground.

It's true that if you want to get more of the earth in the picture, you have to back off. The farther you step back,
the more you can include in the view.

The absolute limit is 50% of the earth's surface. Technically, you have to be at an infinite distance to see that half.