Real time following (a la Will Smith in Enemy of the State) from satellite imagery remains fictional at present.

The balance of coverage vs resolution is largely dependent on satellite constellation altitude. Higher altitude = more coverage but worse resolution. More satellites also gives better coverage, but adds cost. To get enough coverage for streaming at high enough resolution for tracking an individual person needs a) an infeasibly large satellite constellation b) improvements to image resolution so higher altitudes (and thus better coverage with fewer satellites) c) guaranteed clear skies (for imagery data at least).