How to make wallpapers fit different monitor sizes

[mumsloveme69420]

having an issue as I have three monitors, and the top monitor is a 32" and my bottom two are 27", so when I have one wallpaper stretched between the three, the image looks distorted slightly. Is there any way to adjust the resolution or wallpaper size on just one monitor?
It's a little tricky to explain but basically I have a character as the wallpaper and her head looks bigger on the top monitor than it does on the bottom two.
Thanks for any help you can provide!