Well, he's going to have seen pictures of her at around that age, certainly. Her wedding photos, for example....
I would imagine there would be prominent pictures in his house showing Sakura as a young adult, and also that she'd have shown him photo albums and even family videos. He won't have seen anything prior to the Grail War, though, I very much doubt that the Matous went out for family portraits (and even if they did Sakura would probably have burnt them), and I see no indication of Shirou having taken photos with her either.