See 10 of 12 unlockable illustrations in 3D on 3DS.
Note: Please do not continue if you are spoiler-sensitive.
From the Tanooki Suit to the game's name itself, Super Mario 3D Land's links to Super Mario Bros. 3 are numerous. In yet another neat throwback, the game includes letters similar to those that you receive from the Princess at the end of each world in Super Mario Bros. 3.
Unlike the original written letters, these letters are actually "photos" of Peach's circumstances during the game, featuring artwork done in the 2D style of the earlier Mario games. The dozen illustrations include stacked 3D layers, which move around and play sound effects when the 3DS is jiggled. Once unlocked, you can save these shots to SD card. We received ten of the pictures from an unnamed source, and you can see the artwork below (the final two likely come from clearing the extra stages). If you view this page in the 3DS web browser, you will be able to view the following images in 3D by tapping and holding on each image.