blender python: texture change from command line

texture_change.py

'''
texture image path are relative to the blend file directory. run from command line like this:
 
texture=img/2012720989_c.jpg blender -b mug.blend --python texture_change.py -F PNG -s 1 -e 1 -j 1 -t 0 -a
''''
import os

image_file = os.getenv('texture')
if not image_file:
	image_file="img/2012720989_c.jpg"

PIC_obj="PIC"

import bpy
from bpy_extras.image_utils import load_image


bpy.ops.object.select_all(action = 'DESELECT')
bpy.data.objects[PIC_obj].select = True
bpy.context.scene.objects.active = bpy.data.objects[PIC_obj]

image_abs = bpy.path.abspath("//%s" % image_file)

image_name = os.path.split(image_file)[1]
bImg = bpy.data.images.get(image_name)
if not bImg:
	bImg = load_image(image_abs)
name_compat = bpy.path.display_name_from_filepath(bImg.filepath)

material_tree = bpy.data.materials.get("PIC").node_tree
links = material_tree.links

texture = bpy.data.textures.get(name_compat)
if not texture:
	texture = material_tree.nodes.new('ShaderNodeTexImage')
	texture.image = bImg
	texture.show_texture = True
	texture.name = name_compat 

emit = material_tree.nodes['Emission']
links.new(texture.outputs[0], emit.inputs[0]) 

Can you please tell me how the texture file (2012720989_c.jpg) looks like?