Upgrade the Watch OS system of Apple watch to version 2.0 first.
In the Apple watch software on iPhone, go to my watch >; Photos > sync album.
Select the album you want to sync to Apple watch.
In the dial interface, use the Force Touch function to press the dial hard to enter the dial setting interface.
Slide left and right to find the photo turntable, and click the "Customize" button below the turntable to enter the custom settings.
In the custom interface, scroll the digital crown of the circular crown and gently select the photo to be wallpaper.
After all selections are made, press the digital crown of the circular crown twice to confirm. The first time is to confirm the custom settings of the dial, and the second time is to confirm the use of the current dial.