How to span Windows 10 background picture to multiple monitors

To set or extend a background picture to second screen or monitor, use the steps below.

1) Right click your Desktop and click Personalize
You can also search Personalize in Window search box, and click Themes and related settings

2) Under the background tab, select Span in the "choose a fit" drop box.

3) Close and check how your Windows background picture changes

This will span the picture to the second monitor instead of displaying the same picture on both monitors.