The following trailer is for a DSiWare title (Rittai Kakushi e Attakoreda, or Hidden 3D Image: There It Is!) that's set to be released next week in Japan.
The gist of the game: Players tilt their DSis to change their perspective and uncover words (and objects, I think) that are hidden in each picture-book-styled stage.
How is that possible? I have no idea, but someone over on NeoGAF has come up with a pretty plausible explanation: "It's possibly ... using the outside camera and doing color-checking, but I'd wager it uses the front-facing camera and the face-tracking tech," said gamer suggested earlier today.
I can't see Nintendo leaving this one in Japan, so I'm guessing it'll show up on our shores sooner rather than later. Honestly, I'd be more than happy if it showed up later, as I don't (yet) have a DSi and probably won't have one for some time.
For more information on Dimensional Hidden Picture, check out this page on Nintendo of Japan's site and this NeoGAF thread.