Hi okapi - maybe I don't understand the problem, you wrote:

> I just sometimes wish I would have a quicker way to scale
> the images in relation to a given line or square in the scene.

You should already be able to do this, when you drag the corner of an image snapping is enabled to any given line or square in the scene, unless you have possibly turned off Object Snap in the bottom toolbar? If you look at the bottom toolbar, the Object Snap button should be highlighted in orange to enable it.

Here is a quick demo that shows how you can snap an image to an given line or square in the model using object snaps:




Doesn't that do what you need? If not I guess I need some more details.

- Michael