Back to the topic as for those NASA datas, the tiny black spot can't be explained by some optical weakness inherent to such a technology as IMAGE
sat', does it ?
The duration of a satellites orbit is a function of its altitude. Most Low Earth Orbiters orbit at ~350 miles. This gives a period of about 90
minutes, or 16 orbits per day.
Subpoint: The point on the earths surface on a direct line between the satellites Center of Gravity and the earths Center of Gravity. Straight
If a spacecraft is in a polar orbit, it sees the pole 18 times a day, and it crosses over any other subpoint about once in a zillion years. The
satellite orbits, the earth rotates under it, on the next orbit the satellite passes over a different ground track.
If you incline the orbit slightly, the satellite track can be adjusted to repeat itself. It's called a Sun Synchronous orbit.
The typical Sun Synchronous orbit puts the spacecraft over the same track on the earths surface every 18 days. So you can track the path of a plume of
pollutants, or the progress of a disease affecting the coffee crop in Columbia, et cetera.
Consider this: You have a camera on a tripod above a flat item; a painting. You try to focus on the painting. If you focus on the center, you lose
focus at the edges. The edges are at an angle to the center; the distance is greater. If you focus at the edges, you lose focus at the center.
Mount the camera higher. Use a telephoto. You reduce but do not eliminate this effect. Now change the flat item to a sphere. Lens selection is a
compromise between surface are viewed and the ability to get fine detail on the surface.
The spacecraft are built for a purpose. They provide regional planners with information they need about their region. Experience has shown that a 150
mile square is a good size for regional planners.
If the spacecraft is in a polar orbit it eyeballs the pole 18 times a day. Who needs an update on the pole 18 times a day?
If the spacecraft is in a sun synchronous orbit it eyeballs the same track on the ground on a regular schedule. A 150 mile wide swath. But it doesn't
ever cross the poles. The angle of the orbit and the angle of view of the cameras work out so that the camera does not quite see the pole in the edge
of the picture. If the lens on the camera was altered slightly, you would see the poles. But this is not a priority for spacecraft designers.
Hence the tiny black dot at the poles.