The US has surprisingly few restrictions on satellite imagery until you get below ~50cm resolution. Beyond a short list of nations/groups that the US has strict export controls with (e.g. N. Korea), there aren't any restrictions at all on who can be sold imagery. Other countries (e.g. Canada) actually have considerably more restrictions on collecting and selling imagery.
It depends. There is some debate as to how one measures resolution. With nanosats one has the option of taking many low-rez images and combining them into a higher rez. So does it depend on what is taken by the sat or what is delivered to the customer? Or what if the customer is the one combining the images?
Planet Labs is a US company so presumably they have US government approval for their sats. Their resolution is really low by today's standards so their imagery may not be considered sensitive. Or maybe they just blur out the same things that every other satellite company blurs out.
