Instructions
Press the "Start" key on your keyboard and type "Run" in the field. Press "Enter" when the search result appears, opening an instance of the Run program.
Type "%appdata%" into the field and press "Enter." This opens up your Application Data folder, listing numerous folders that are otherwise hidden by default.
Double-click ".minecraft," followed by "bin." Right-click "minecraft.jar" and select "Open With," followed by your preferred extractor. A list of the folders inside the JAR file will appear in your extraction program.
Double-click "art" to reveal the only file inside: kz.png. Drag this file to your desktop to extract it, and then double-click the file to open it in your preferred editing program, such as MS Paint. This opens a file with all of the different paintings available in the game.
Modify any of the pre-existing paintings in the file as desired. This can include painting over already existing pictures or pasting your custom-made painting on top of an old painting. Save the file when you are finished.
Click "Add" on your file extractor, which opens a dialog box for you to add new files to the archive. Double-click the file you modified on your desktop, and then click "OK." The archive will save, and you can display your custom painting just like a normal painting in "Minecraft."