Earth in this image has a diameter of around 5 pixels. So each pixel here is around 2500 km (as diameter of earth is around 12700 km [1])
Farthest human has been is 400,000 km [2]. So the farthest we have ever been is around 160 pixels.
[1] https://www.google.co.in/search?q=diameter+of+earth&oq=diame...
[2] https://en.wikipedia.org/wiki/List_of_spaceflight_records#Fa...