Paintings are items in Minecraft that are used as decoration. They are also used to make secret hideouts. There are 24 different types of pictures, from 1x1 blocks to 4x4 blocks. If hit with any throwable item (such as an egg), it will drop an an item.
Paintings are mainly used as decoration, but experienced player use them to make secret entrances. To put paintings on doors, press sneak (default LeftShift) and place the painting. Then, cover the whole building in paintings. Note: Keep the door open when your outside otherwise you wont be able to get in. When your inside, close the door so no griefers come in.