Google Page Speed – Optimize Images for mobil devices

Hi WordPress Community,

I’m running this great site for canyoning adventures in Germany. Now Google Page speed Insights tell me that I need to optimize my fotos, especially for mobil devices.

Now how do I do that? Because if I reduce the size of my fotos even more, then they won’t be suitable for desktops any more. Do you have any ideas?

THanks and regards

Chris