This probably doesn't fit into the performance aspect of amp. It is however an often used stylistic effect to have images parallax scrolling. This, of course, doesn't work on mobile yet and is often a problem on desktop browser too so it would be challenging. However: a correct implementation could make this effect much more pleasant.

I imagine it like this:

<amp-parallax width="1200" height="630" layout="responsive">
    <amp-img src="/image.jpg" width="1200" height="1260" layout="responsive"></amp-img>
</amp-parallax>