> Is it possible to scale a background image not only from the center
> and the edge points but from a custom reference point ?
Yes, you can use the Align function inside the View > Image command for that:
That will allow you to pick 2 reference points on the image, and then 2 points in the model and the image will be scaled and rotated to match up the lines. If you want only scaling and not rotation make both lines horizontal or both vertical.
