Looks oddly familiar. Probably the poster included in the upcoming Musume Type mentioned in DevTweet, since I recognize her from their newest user avatar (which is usually a teaser image of sorts).
If an artist made an art for a character that s/he was contracted for, it's not automatically 'official' art unless there's the (c) sign that represents that art was made for the job. Else for that it's just art.
Kadokawa's artist drew Kadokawa's character in a magazine published by Kadokawa. How is this not official just because there's no copyright sign?