I think a lot of people like to customize their Windows 10 systems and Microsoft makes that very easy through the Windows Settings > Personalization settings page.
However, there is one customization that is not real obvious on that settings page that allows anyone with a multi-monitor system to actually assign a different wallpaper to each screen as their wallpaper.
Step One: Open up Windows Settings > Personalization
When you open Windows Settings > Personalization it opens to the Background settings by default.
Of course, you can click on any one of the displayed images, the last five you have used are shown, or you can select Browse to use one stored on your local drive(s).
Step Two: Select Wallpaper for Each Monitor
As you can see in the image above, if you Right Click on any of the displayed images you will get a Context Menu that lets you select that image for all monitors or other monitors on your system. Although I have not tested it, this should work if you have more than two monitors on your Windows 10 system as well.
If an image you want to use as a background on a specific monitor is now shown you will have to select it using the Browse button and then use the context menu to place it on a specific monitor. Repeat as necessary to get your monitors each their own specific background.
Here is a massive (3840 x 1080) screenshot of my dual monitors sporting two different images as their background wallpapers.
Be sure to check out all of our Windows 10 Anniversary Update Coverage.