Desktop background style: Fill
since 0.9.8.11
Purpose
Show registry keys (1)
HKU\.DEFAULT\Control Panel\Desktop\WallpaperStyle
The WallpaperStyle string value set to 10 selects the Fill presentation mode for a desktop background image. Windows scales the image proportionally until it covers the entire display area, then crops any portions extending beyond that area. The image's aspect ratio is preserved.
This value controls presentation only. It neither selects a background image nor modifies the image file.
Notes
Possible side effects
When the aspect ratios of the image and display area differ, parts of the image are not visible. Scaling a low-resolution image up to cover the display can also reduce its perceived sharpness.
Notes
WallpaperStyle is a REG_SZ value. The value data 10 represents the Fill mode on Windows 7 and later.
Despite its name, HKEY_USERS\.DEFAULT is not the template for newly created user profiles. This hive belongs to the LocalSystem account and therefore does not provide a general desktop default for signed-in users. The actual default user profile is stored under C:\Users\Default; its NTUSER.DAT file is not normally mounted as HKEY_USERS\.DEFAULT. If the intended purpose is to preconfigure new user profiles, the specified registry path does not identify that profile template.
Microsoft documentation
Microsoft Learn: Theme File Format
Microsoft Learn: Customize the default user profile by using CopyProfile
Microsoft: The .Default user is not the default user