That instagram account has been around for months and months. I scrolled back to February and recognized art from dozens of major Klaine fanartists there, and quite a few screencapped fic intros. If you are a fanartist or if you write NC-17 fic especially on LJ, you should scroll through that account and follow this link to report copyright violation of any of your own work that you find. This is not something that affects just a couple of people. This is like every major artist in this fandom.
This is so disappointing and my sympathies go out to all the fanartists (and fic writers) personally affected. Fandom rarely repays its artists of either sort the way that it should, but art thieves are a horrible reminder of the very worst side of the fandom.