Fawkes and Codex "Highland Sextasy." Original art by Greg Aronowitz
As seen in Season 4, Episode 3 of The Guild.
Artwork by Greg Aronowitz. Follow him on Twitter @gregaronowitz and visit his Barnyard FX blog.
There's an 18" x 24" poster of this, which debuted at Comic-Con 2010. Available for purchase from Think Geek.