Despite an easy start with the mobile layout, when it came to swapping out the mobile image for the desktop image, I found this quite tricky. In the end I used an empty div and the background-image css property to swap this around. One bonus this approach had was that it allowed me to add the purple overlay (via background-blend-mode) without the need for an additional div over the top. In the end I sized the empty img div using fixed pixel measurements - however, this doesn't feel responsive or eloquent, so I'd be interested to hear how else it might have been done.
Thanks!