This module is just the solution for that problem.
Add images to a module positions with some specific parameters and add separated variables for mobile.

In the mean time it's grown out to be a very mature module, with all kinds of extra features added. Use an overlay or even a second one to make your headers not only look nice with stuff like gradients or color overlays, but also provide it with functional content like texts or images.

You can now also use it at any module position and more than ones on every page or module position.