It's nice and all that you're not claiming this piece to be your own, but I'm sorry, doing something like this is not acceptable. On DA " you must post your own original works" - from the DA policy. I'm not sure what not knowing people has to do with keeping stolen artwork up....but I'll try to consider that?
And calling me childish? This is very serious matter, there are people out there making their living off of art work and another person is getting credit for their work. If it is serious enough, things like this can get legal; so I'm trying to give you head up before you get charges or even a lawsuit set against you in the future. Niconoff is a professional concept artist so his works are all copyrighted, saying sorry isn't going to alleviate anything.
Past or not other people's artwork are still currently posted in you gallery. So it's still considered a present day situation to be dealt with >n> I'm not going to badger you anymore or let myself get mocked for defending the rights of other artists, so I'm going to let the Admins handle this.