There has been ongoing speculation on here and TES forums about whether this is supposed to depict a Hagraven/a stage of Hagraven development OR the Daedric Prince Nocturnal
I can say with fairly high confidence that this IS concept art for a Hagraven
The Bethesda Flickr account uploaded this image in the same batch as number of concept pieces for the developmental stages of Hagravens.
This/those pieces were also uploaded amongst a larger group of "monster" concepts eg. Hagravens, draugr, dragons, etc.
Lastly Adam Adamowicz did not do any of the concept art for Daedric princes or shrines for Skyrim. That specific responsibility on the Skyrim art team was actually held by Ray Lederer who did all the daedric shrine concept art.
Unfortunately I've never seen any Nocturnal concept art for Skyrim, but if it exists, the creation of it would not have been Adam's responsibility as part of Skyrim's art team
