My recollection is Windows 98 popping up a box like “Click yes to enable Active Desktop to do this” when I had AD disabled and tried to set a JPEG wallpaper. Th

My recollection is Windows 98 popping up a box like “Click yes to enable Active Desktop to do this” when I had AD disabled and tried to set a JPEG wallpaper. That would imply SHELL32 >= 4.7 https://www.geoffchappell.com/studies/windows/shell/shell32/history/index.htm?tw=406px https://www.geoffchappell.com/studies/windows/shell/shell32/... Wikipedia sez “Since Windows XP, if a non-BMP image is used as Windows Desktop wallpaper, Windows will convert non-BMP image to BMP image in background.” and Group Policy has some relevant options: “Enable Active Desktop” (“ForceActiveDesktopOn”) https://admx.help/?Category=Windows_11_2022&Policy=Microsoft.Policies.WindowsDesktop::ForceActiveDesktopOn https://admx.help/?Category=Windows_11_2022&Policy=Microsoft... has the description “Allows HTML and JPEG Wallpaper”. Also “Allow only bitmapped wallpaper” (“NoHTMLPaper”) option: https://admx.help/?Category=Windows_11_2022&Policy=Microsoft.Policies.WindowsDesktop%3A%3Asz_DWP_NoHTMLPaper https://admx.help/?Category=Windows_11_2022&Policy=Microsoft... “If users select files with other image formats, such as JPEG, GIF, PNG, or HTML, through the Browse button on the Desktop tab, the wallpaper does not load. Files that are autoconverted to a .bmp format, such as JPEG, GIF, and PNG, can be set as Wallpaper by right-clicking the image and selecting "Set as Wallpaper".” Both “Supported on: Windows Server 2003, Windows XP, and Windows 2000 only”.