import os
DIR ="/home/path/to/folder"
bg_file = os.path.join(DIR, "myimage.jpg")
bg_img = bpy.data.images.load(bg_file)
bpy.data.scenes['Scene'].render.filepath = os.path.join(DIR, "image")
bpy.context.scene.camera = bpy.data.objects['Camera']
bpy.ops.render.render(write_still=True)

import bpy
filepath = "/home/path/to/folder"
img = bpy.data.images.load(filepath)

for area in bpy.context.screen.areas:
    if area.type == 'VIEW_3D':
        space_data = area.spaces.active
        bg = space_data.background_images.new()
        bg.image = img
        break

cam = bpy.data.cameras.new("Camera")
cam_ob = bpy.data.objects.new("Camera", cam)
bpy.context.scene.camera = cam_ob
bpy.context.scene.objects.link(cam_ob)
bpy.context.scene.objects.active = bpy.context.scene.objects["Camera"]

import bpy
bpy.ops.import_image.to_plane(files=[{"name":"starfield.jpg", "name":"starfield.jpg"}], directory="/home/eli/Pictures/Blend/Python/")
bpy.context.object.scale[0] = 9
bpy.context.object.scale[1] = 16
bpy.ops.transform.translate(value=(0, 0, -3))

import os
import bpy

DIR ='/home/eli/Pictures/Blend/Python/'
bg_file = os.path.join(DIR, 'starfield.jpg')
bg_img = bpy.data.images.load(bg_file)

for area in bpy.context.screen.areas:
    if area.type == 'VIEW_3D':
        space_data = area.spaces.active
        bg = space_data.background_images.new()
        bg.image = bg_img
        break

bpy.data.scenes['Scene'].render.filepath = bg_file
bpy.context.scene.camera = bpy.data.objects['Camera']
bpy.ops.render.render(write_still=True)

bpy.data.worlds['World'].node_tree.nodes['Background'].type
'BACKGROUND'

bpy.data.worlds['World'].node_tree.nodes.new('bpy.types.ShaderNodeBackground(img)')