1
Open the Settings App, then go to Personalization - Background.
If the 'Personalize your Background drop-down menu is set to Windows Spotlight, set that to Picture and select your preferred image.
2
If that was not the problem, in the Settings App, go to Personalization - Themes.
If that is set to some active theme, set the theme to the default Windows Theme.
Then go back into the Background setting and set your preferred background image.
3
If neither of those were the cause of the problem, open the Settings App, then go to Apps - Installed apps
Check the list of installed apps to see if the Bing Wallpaper app is installed, if it is, uninstall it.