You can capture still lives and portraits in tabbed mode; the trick is to press Tab
before the game prompts you to capture the image for the painting. And you can move around to capture a portrait after pressing Tab, so you can get past any walls. I always play with walls up and make sure to position the camera close to the subject before I press Tab. I find that easier; no risking having to navigate through walls.
It doesn't work if your sim is taking photos though. Believe me, I tried.
Speaking of putting your walls up, that's my biggest screenshot tip. Well, I could just quote Lisey for my reasoning:
-First, walls up. I suppose this is more of a roleplay thing, like do you want your photos to be obviously from a game or not? I'm obsessed with making sure that walls and ceilings are up.
It also make the backgrounds of your screenshots far less cluttered. Instead of seeing multiple rooms because your walls are down/cutaway, you get the walls instead. And it means that people get to appreciate my choices in wallpaper when they see my screenshots. Also, I'd rather not ruin emotional scenes that happen in my sims' dining room because the walls are down and exposing another sim using the bathroom the next room over.