How about making it resizeable as the product images are?
Here is a use case when this might be needed:
One category has the layout 2-columns left.
I have one image that fits in this format.
I take the decision to change the layout for that specific category to 3columns. I have to reupload an image in the correct size, to fit in the new layout.
But if the image was resizeable, I could just change the resize values.
The resize values can even be 2 attributes in the backend, so when I change the layout I can change the width and height as well.
If these attributes are empty then the image is shown at full size.