If you are in the setup mode for Match Photo, moving the origin is really more like moving the image relative to SketchUp's fixed origin. You would set the axes so that the origin aligns with some easily identifiable corner in the image.
You might find it easier to set up the Match Photo image in a separate file and then copy the model into that file to place it where you need it.
If you share the SKP file of your model and the image you are using, I can give you more specifics.
