What the difference between Taekwondo from North Korea and South Korea?

North Korea is with the ITF style of TKD. It's not like ITF is North and WTF is South type of a thing. There are ITF members in the South and all around the world. It's just that WTF used to(possible that they still do) work closely with the South Korean government so the WTF TKD was never promoted nor wanted in North Korea. You don't see North Korean TKD in Olympics because the Olympic TKD goes by the WTF ranking.

As for actual martial arts, I don't think there is much of a difference. I would guess that ITF is more North, while WTF the Olympic style is more South (that is PURELY guessing), however, the form Juche was added in to ITF in order to promote more North-South Korea unity. That leads me to believe that in general, there is not much difference between the arts coming from both countries even if you argue the North does ITF due to its more pro Japanese attitude, while the South, being more secular, thus geared to the Olympics, does WTF. Now this article validates my guess of North/ITF South/WTF: http://gwdprk.blogspot.com/2008/06/nkorean-tae-kwon-do-south-korean-tae.html The differences in ITF and WTF taekwondo are 1) different forms and 2) in competition, WTF does mostly/all kicks. ITF looks more like Japanese Karate (even has one of the same forms), and was pretty much "karate" until General Choi added in the Sine Wave (which I hate personally, but will practice it so I can teach it, and I have used it from time to time, just not in an exaggerated way). As for gruesome inhumane abuses of the martial art of Taekwondo, well, there are stories about guards using prisoners as practice dummies: http://www.businessinsider.com/north-korean-prison-camp-guard-i-watched-dogs-rip-children-to-pieces-2014-2

I don't think North Korea allows them to do martial arts.. one reason is they are closed of from the world and also they cant leave and come as they want.. If they do train in martial arts its most likely military only..