#region  To obtain windows Desktop background
        [System.Runtime.InteropServices.DllImport("user32.dll", CharSet = System.Runtime.InteropServices.CharSet.Auto, SetLastError = true)]
        public static extern int SystemParametersInfo(int uAction, int uParam, StringBuilder lpvParam, int fuWinIni);
        private const int SPI_GETDESKWALLPAPER = 0x0073;
        #endregion

void WindowsBtn_Click(object sender, RoutedEventArgs e)
        {
            // Define the size of the storage buffer
            StringBuilder s = new StringBuilder(300);
            // To obtain Window  Desktop background image address, using buffer
            SystemParametersInfo(SPI_GETDESKWALLPAPER, 300, s, 0);
            // Characters in the buffer are converted
            string wallpaper_path = s.ToString(); // System desktop background image path
         }

Call windows api get

Note that the size of StringBuilder should not be less than 255, because the windows path supports a maximum of 255. If the definition is too small…

Returns empty if the current system desktop has no background or is a solid color.