Wordpress - page insights- Optimize images for mobile

I'm getting a "Compressing and resizing ..." notification at google page insights. I'm well aware of compressing in photoshop, the thing is mobile images seems to need more compressing than the ones on desktop. 1. is there a way to display different images for mobile? or is there another way to solve this? 2. I've tried smush it plugin, doesn't seem to work