Painting

Paintings in Minecraft are simple, low-resolution versions of a canvas; they currently appear in Beta, Alpha, Infdev, and Indev. Most of the twenty four (19 in indev and infdev) current canvases are by Kristoffer Zetterstrand and are shrunken to a low resolution to fit Minecraft's graphical theme. 5 more are edits or new paintings. A random image from among these is chosen each time a painting is placed. Paintings currently are not flammable, nor do they stop light or players from passing through if blocks behind them are removed after their placement. Paintings can only be placed on flat, vertical surfaces. An easy way to get a painting to fill up the area you want is to place it in the bottom-left corner. It expands canvas size to the top-right to fill up the wall the best it can, though it may still take a few tries to get a large painting.

Crafting
Unfortunately, as of Beta 1.2, you may NOT place paintings as "Secret Doors." They revert back to item form when the player walks through them.

Paintings are the only objects in the game that can simultaneously exist with water in the same block as itself.

Canvases
There are currently 19 canvases in Indev, but there are 24 in Beta. These are mostly based on paintings by Kristoffer Zetterstrand, who also created the Minecraft versions.

Bugs

 * It is possible to get two paintings from destroying one painting.
 * Used to be indestructible in SMP, only dropping "fake" paintings every hit, which could not be destroyed or picked up - but this was fixed in Beta 1.2.
 * Players used to be able to walk through paintings (as secret doors), but this was fixed in Beta 1.2
 * When a painting is placed it sometimes shows a four by four area of solid purple with darker purple between each block. This may possibly be the new painting that Notch mentioned would be added in Beta 1.2_01