As seen in the screenshot; 1st turn of a new game with a custom faction/sovereign.  For some reason, the picture of the sovereign (in the box at the lower right) is replaced with a picture of a box.  The XML for the sovereign contains the following lines which seem to be relevant to creating that portrait:

        <ClothPoseIndex>2</ClothPoseIndex>
        <InfoCardBackground>BG48_Ruins</InfoCardBackground>
        <InfoCardBackgroundFlipped>0</InfoCardBackgroundFlipped>

I can post the full XML for the sovereign, or a savegame, if desired.