The last image of deans route is the kiss at the end of the date if you have enough affection with him. If it's the one after that, it's Hoss's route when you have high affection with him and talk about swimwear by the pool.
The last image in the Trauma you get either from Rosswel's route or from one of the endings progressing towards the true ending.
Oswin in the normal gallery, i'm not quite sure what you mean. You mean with him sitting infront of you next to the candles? You get that when you meet up with him to ask questions, changed to your first in person meeting with him.