Help with responsive images for Bootstrap jumbotron

I recently stumbled upon an open-source version of the Command and Conquer video games on Github, I downloaded it and it was great but I noticed their website was kind of dated. I got bored yesterday and figured I’d remake the website for fun/practice and maybe submit it and see if they want it. This would be my first open source contribution if accepted.

I’m running into some issues with getting a big image to fit the Jumbotron correctly. I’ve tried various CSS tricks like background: auto 100%, background: 100% 100%, background: cover, etc… but can’t seem to get the image to scale well on all devices.

Should I be using different size images for different devices? If so, what are the common sizes for a picture to look good on a small/extra small devices?

Here’s how it currently looks on an Iphone and my Pro Retina screen:

And here’s the Iphone look: