https://learn.microsoft.com/ja-jp/dotnet/api/system.windows.media.imaging.bitmapframe.baseuri?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-10.0
BitmapFrame.BaseUri Property (System.Windows.Media.Imaging) | Microsoft Learn
When overridden in a derived class, gets or sets a value that represents the base Uri of the current context.
property systemwindows mediaimagingmicrosoftlearn