Use your own wallpaper
Go to Settings > Desktop and Wallpaper > Wallpaper and select a picture. Select blur and preview effects as needed, click Apply, and choose to set them as lock screen, desktop, or both.
Set the photos in the photo gallery as wallpaper.
Enter the gallery and find your favorite picture. Click the four-point icon > Settings > Wallpaper, and complete the settings according to the screen prompts.