Hi Garudin,
It’s great to know that you are using Windows 8 and thank you so much for posting this query in the Microsoft Community Forums!
You would like to know on how to set a picture as the desktop background from the Photo App and also on how to set separate pictures as backgrounds on
different monitors connected to the computer without using any third party software.
We’ll not be able to set a picture as the desktop background from the Photo App. Since it isn’t possible to set the wallpaper from the photo app, you can leave a
feedback within the app.
This can be done by pressing “Windows Logo” + “C”, clicking on “Settings” and then “Feedback”.
We will also not be able to set different pictures as backgrounds on different monitors connected to the computer.
Hope this answers your queries.
Thank you.