How to place an image placeholder that scales the image to the full frame size in a template

[Cube]

I'm trying to set-up a template with an image placeholder that, when you insert the image, scales the image to the full size of the placeholder. I tried a table with fixed settings, but the image never scales to the full frame size. It scales,but not to the complete with of the frame. (I used odd dimensions, 29.7 cm wide and 10.5 cm high on a landscape page)


Is there any way to accomplice this?

Help is super welcome. I've been Googling for hours/days now