The diameter of the Earth is 12,742 km. Most images of the whole Earth are only at most a few thousand pixels in diameter. So any satellite or space junk will be only a fraction of a pixel so invisible unless it is of order of a kilometer in diameter or more. So far we don't have anything that large.
Only chance of seeing them would be in the dark sky around the Earth - but then they would be indistingishable from stars, so you'd need to know your constellations very well. And anyway - most of those images are exposed in such a way that the stars can't be seen, because the brightness levels are adjusted to show details on the much brighter Earth.
The ISS is about the size of a football field, about 108 meters in length.
To resolve it with a width of, say, 2 pixels, you'd need a picture of the Earth more than 250,000 pixels in diameter. Or a total of 62,500,000,000 pixels.
The largest images made would be high enough resolution to see the ISS.
Anything with more than 60 gigapixels or so would be able to show the ISS as a couple of pixels or more in an image of the world.
E.g. this 320 gigapixel image of Mont Blanc
Page on in2white.com
If someone produced an image of the Earth to this resolution, the ISS would be about 4 to 5 pixels across.
But you'd only see it if you knew where to click to zoom in. And that's pretty small so it would need to be noticeably different in colour or some such to spot it.
More examples here: Largest photographs in the world
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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