A good cover image speaks volumes about you.
If you look at the F1 Visa Facebook Group, I change the images every few months.
You know know what information do you want to convey with your image.
Here’s are good places to find stunning images. And if you get get stencil, you can add some text it it.
Maybe you have a git or web page that you can list it.
Maybe pick an image that reflects your academic background.