Documentation

Setup:
To use the node, first you need to download the blend file (CompositorPaintBlend.blend) and click Append in the file you want to use it in. Then, select the CompositorPaintBlend file, go to NodeTree, and double click on Paint. This will add the paint node into your file. To use it in your scene, enable Use Nodes in the compositor. Then, create a Paint node. For the input, use the Image output of your Render Layers node, and plug the image output of the Paint node into the Composite node. Now you should be ready to start messing around with input values.

Node Inputs (And What They Do)
Scale - Changes the scale of the displacements and warping being done to the image. This does not change the bump-map overlay.
Secondary Scale - Changes the scale of the bump-map overlay. This will not physically warp the image, but will change some of the characteristics.
Contrast Amount - Changes the image contrast according to the overlay texture.
Speckling Amount - Determines how much of a speckling there will be to the image. A small amount will give a realistic look, while a large amount will give a more stylized/blurred look.
Speckling Scale - Determines how large the speckles in the image are.
Shadows - Changes the intensity of the shadows on the bump-map overlay.
Primary Displace Scale - Changes the intensity of the physical displacements in the upward and right directions.
Secondary Displace Scale - Changes the intensity of the inverse displacements in the downward and left directions.

How To Use Custom Overlay Textures
Overlay textures are the textures that are used to apply texture and depth to the renders with this node. As unfortunate as it is, I could not find a way to have an image input work for the texture (since the mapping of the image is changed for better results), however you can still change the overlay texture. Navigate to the Textures tab on the right sidebar, and select the Brush Overlay texture. Now, simply change this to whatever texture/image/pattern you want, and the Paint nodes will apply that texture to the images.

Any Other Questions?
If you have any other questions about the Compositor Paint node that have not been answered, or you are having any trouble with getting it to work, please contact me and I will work with you to answer the question or get the issue resolved.