What if the screen is too wide (like 27 inches) and the photo resolution is not good enough? Is there any best practice for this feature?
It all depends on your audience.
Professional designers? Yeah, they'll make sure the graphic is awesome. Professional artists with management and social media teams? Of course they will.
Your average user? Absolutely not. They will grab whatever photo they usually use or some random one from profilephotoplacewithglitter.com and be done.
If you want your site to look good, don't depend on the user for anything.
Source: My facebook friends.