well, you can post "screenshots" of a game you're playing in the game's community. I.e.: play SM3DL, home menu, go to miiverse, then make a post in the 3d Land community and you'll see a screenshot button.

when you are playing a game, suspend the software and open miiverse and open the game's community. then make a post and click the image icon and pick any of the 2 pictures (top and bottom screens) if you are on 3ds and then post the picture.