Watermark

Watermark is a common name for a label on the bottom-right corner of the Windows desktop identifying the operating system version, which overlays the desktop wallpaper. It is most commonly associated with pre-release versions, where it is enabled by default with no option to disable it unless one modifies the system files. It is possible to enable it on release builds by modifying or adding a registry entry. A distinctive form of watermark is also visible when a Windows system boots in safe mode, overriding any other forms of watermark, if applicable. Debug builds will also display the path to the currently loaded Windows installation below the version information.

Watermarks originally used to be displayed on checked/debug builds only. Since the development of both Windows 98 and Windows 2000, they have become widely used to mark pre-release builds regardless of the build type.

History
The first Windows build known to display a kind of watermark is Windows 3.0 Debug Release 1.14; it was later removed in the lead up to the RTM. Watermarks were reintroduced during the development of Windows 3.1 as seen in the SDK debug kernel which, if applied on top of an existing copy of Windows, displays a shaded label in the bottom right corner identifying the current operating mode and the Windows version. The details of the current operating mode were removed during Windows 95 development, as they became redundant with the removal of Standard mode and 286 support.

Watermarks did not appear on non-debug builds until Windows 98 build 1351 and Windows 2000 build 1989.1. Enabling Active Desktop would remove the watermark until it was disabled. Starting with Windows 8 build 7788, internal builds also display a seperate message stating that the software is Microsoft confidential material, in addition to warning users about the legal consequences for leaking these builds outside of Microsoft. A similar message was also shown in. The last known build to contain this warning message is Windows Server 2016 build 10587.

PaintDesktopVersion
In Windows NT-based builds that do not show the watermark by default, it is possible to enable it through the  registry value:

Windows 98 and ME use a string value instead: