Automatic script for Displacement in 2.5

Hello,

I want to do something like this :
start Blender with a script (2.5 version) with 2 parameters : input_image, output_image.

How to :
command line ? :
Blender -P myscript.py input_image.jpg output_image.jpg ???

In the script, should do something like :

bpy.ops.image.open(input_image) ?

Make a plane…then…

???
bpy.ops.uv.unwrap()
bpy.ops.material.new()
bpy.ops.texture.new()

displacement ?

bpy.ops.screen.render(output_image) ?

Can you help me, because no tutorials on scripting with 2.5 API until now …

Thanks

Alain