For 1.21 and up check the New Custom Paintings Resource Pack and Datapack using the new Painting variants feature

Custom paintings resource pack

This Minecraft resourcepack adds some new paintings by using the CustomModelData feature added in 1.14.

It is inspired by the custom paintings used on the Hermitcraft server, as seen in this video (14:53).

Installation

Install like any other minecraft resource pack.

Usage

The following image shows the paintings available in the resourcepack. You can also add your own.

Available paintings

To get the paintings you have two options: using the give command or using mukitanuki's Custom Roleplay Data datapack.

Give command

Use the following command to give the player the custom painting defined by the CustomModelData number.

/give @p painting{CustomModelData:<number>}

Where <number> is the painting index as defined in painting.json

mukitanuki's Custom Roleplay Data datapack

Alternatively, and more survival friendly, CurseForge user mukitanuki has created a datapack to change an items CustomModelData tag. You can download it from CurseForge.

Once installed you can run the command /trigger CustomModelData set <number> changing <number> for the index of the painting.

Check the CurseForge page for complete instructions on this datapack

Adding custom paintings

Paintings in this resourcepack are composed of 16 by 16 pixels tiles, although the texture can be upscaled.

Textures

Place your textures (in png format) into assets\minecraft\textures\item\paintings directory inside the resource pack. They can also be placed inside their own subdirectory to keep them organized.

Models

Create a new .json file for each painting you want to add in assets\minecraft\models\item\paintings. You can also place this files inside of their own subdirectory.

Copy and paste the next code into the file you just created and change the text between quotes after the following properties:

{
    "parent": "item/paintings/master_painting",
    "credit": "YOUR_NAME",
    "texture_size": [16, 16],
    "textures": {
        "0": "item/paintings/YOUR_TEXTURE",
        "1": "painting/back",
        "particle": "item/paintings/YOUR_TEXTURE"
    }
}

"credit": Change YOUR_NAME for the message to credit you with this painging.
"texture_size": Change this numbers if your painting is not 16 by 16 pixels.
"0" and "particle": Change YOUR_TEXTURE for the name of your texture withouth the .png extensions. If you placed the textures inside of a directory you also have to include it.

Adding models to the painting

Edit assets\minecraft\models\item\painting.json and add a comma after the last predicate line and paste the following code.

{"predicate": {"custom_model_data":MY_INDEX}, "model": "item/paintings/MY_MODEL"}

Change:

MY_INDEX: for the index of the new painting, make sure they are not repeated or it will override another painting.
MY_MODEL: change my model for the name of the .json file you created in the previous step, without the file extensions. If you placed your file inside of a directory remember to include it as well.

Credits

First 4 sample paintings in the resource pack are created from art released under CC0 license by ansimuz. You can find the original images at the next links:

Painting 1 "River" - Top Down River - Shooter Environment by ansimuz
Painting 2 "Forest" - Forest Background by ansimuz
Paintings 3 and 4 "Mountain" - Mountain at Dusk Background by ansimuz
Paintings 5 to 10 "Road" - Country Side Platform Tiles by ansimuz

The rest of the paintings are created based on public domain images. You can find the originals in the next links:

Paintings 11 to 14 "Port" - Cumulus Clouds, East River by Robert Henri
Paintings 15 to 26 "Bridge" - Florence by Henryk Dietrich
Paintings 27 to 30 "Sunset" - Sunset by Frederic Edwin Church
Paintings 31 to 32 "Fairy Nebula" - The Fairy of Eagle Nebula by NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
Paintings 33 to 36 "Cone Nebula" - Cone Nebula/NGC 2264 by NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA
Painting 37 "Flowers" - Still Life with Flowers in a Glass Vase by Jan Davidsz. de Heem
Painting 38 to 41 "Temple" - brown high-rise building by Lucrezia Carnelos
Painting 42 "Sun" - After the Deluge by George Frederic Watts

Custom Paintings