Blizzard_TalentUI creates
PlayerTalentFrame, which it marked as LoD.
Blizzard_TalentUI.lua:248 calls
SetPortraitToTexture(), which is the function that applies the circular mask. This line specifically sets the icons for the spec list on the left side. For the details pane,
line 1156 sets the spec icon in the description and
line 1267 sets the icons for the ability list.