As with most things in Bubble (and programming in general), there are likely several viable approaches. @adamhholmes made a good suggestion.
Another possibility is to use the Align to parent layout mode. It seems well suited, as it enables positioning of elements relative to the center, corners, and middle of each side (the so-called “nonants”). Using an actual image element might also offer some advantages, such as specifying a fixed aspect ratio while still enabling the image to change size at different page widths…
Note, however, that the layout engine is still in beta, and there are some rendering glitches as the page is dynamically resized. Refreshing the page at any given width will cause the layout to re-render correctly.
(Also, for future reference, there’s a forum dedicated specifically to the new responsive engine.)