Houdini set node image thumbnail (NetworkView background image) and attach / link it to the node through Python

hou_set_node_thumbnail.py

import hou
import contextlib


@contextlib.contextmanager
def editor_at_node(node, pane_tab_type=hou.paneTabType.NetworkEditor):

    editor = hou.ui.paneTabOfType(pane_tab_type)
    original_pwd = editor.pwd()
    try:
        editor.setPwd(node.parent())
        yield editor
    finally:
        editor.setPwd(original_pwd)


def set_node_thumbnail(node, image_path):

    with editor_at_node(node) as editor:
        images = editor.backgroundImages()
        images = list(images)
        
        node_path = node.path()
        # Find existing image attached to node
        image = next(
            (
                image for image in images if
                image.relativeToPath() == node_path
            ),
            None
        )
        rect = hou.BoundingRect(-1, 0.2, 2, 2)
        if image is None:
            # Create the image
            image = hou.NetworkImage(path, rect)
            image.setRelativeToPath(node.path())
            images.append(image)
        else:
            # Update existing image
            image.setRect(rect)
            image.setPath(path)
        
        editor.setBackgroundImages(images)


# Example usage
node = hou.node("/obj/geo1")
path = "/path/to/thumbnail.png"
set_node_thumbnail(node, path)