WPF ImageBrush 转换
GIF图片
<ImageBrush x:Key="ImageLoadingBrush" >
<ImageBrush.ImageSource>
<BitmapImage UriSource="pack://Application:,,,/chatres;component/Resources/ImageLoading.gif" />
</ImageBrush.ImageSource>
</ImageBrush>

System.Windows.Media.ImageBrush imageBrush = this.Resources["ImageLoadingBrush"] as ImageBrush;
System.Windows.Media.ImageBrush如何转换成System.Drawing.Bitmap?或者Byte[]都可以

[解决办法]

   var image = System.Drawing.Image.FromFile("..."); // or wherever it comes from
      var bitmap = new System.Drawing.Bitmap(image);
      var bitmapSource = Imaging.CreateBitmapSourceFromHBitmap(bitmap.GetHbitmap(),
                                                                            IntPtr.Zero,
                                                                            Int32Rect.Empty,
                                                                            BitmapSizeOptions.FromEmptyOptions()
            );
      bitmap.Dispose();
      var brush = new ImageBrush(bitmapSource);    

[解决办法]

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            System.Windows.Media.ImageBrush imageBrush = this.Resources["ImageLoadingBrush"] as ImageBrush;

            var bitmap = GetBitmap(((BitmapSource)imageBrush.ImageSource));

            bitmap.Save("E:\\茉莉花.jpg");
        }

        Bitmap GetBitmap(BitmapSource source)
        {
            Bitmap bmp = new Bitmap(source.PixelWidth,source.PixelHeight,PixelFormat.Format32bppPArgb); 
 

            BitmapData data = bmp.LockBits(new Rectangle(System.Drawing.Point.Empty, bmp.Size),ImageLockMode.WriteOnly,PixelFormat.Format32bppPArgb);
            source.CopyPixels(Int32Rect.Empty,data.Scan0,data.Height * data.Stride,data.Stride);
            bmp.UnlockBits(data);
            return bmp;
        }

我注意到你的输入格式是gif。WPF只能显示gif动画的第一帧，如要让它动起来，可参考我的《WPF支持GIF的各种方法》。

上面的代码疑似不能处理gif，jpg是可以的。