I herd a commentator talking about this picture many hours before it was taken, and there was quite a bit of discussion as to whether he would smile, look serious, etc. One point made that I think is true was that no matter WHAT the look of this picture, it will become an iconic picture in history. The only President who ever had a mug shot taken, etc., etc.
The New York Times' Maggie Haberman made an interesting and a revealing observation this evening when she said that when Trump was getting his official White House photo taken prior to his inauguration, he scowled at the camera and told aides he though the looked "like Churchill." I think he probably thinks this mug shot makes him look like Churchill, and he thinks he may be remembered by history in the same way Churchill is viewed.