public static void SaveUIElementToJpegImage(UIElement element)
{
    // todo: pass myChart as a command parameter declaratively to be handled in PlotViewModel
    var b = new WriteableBitmap(element, null);
    using (var s = GetLocalFilestreamFromFileDialog(".jpg"))
    {
        if (s != null)
        {
            SaveBitmapToJpeg(b, s);
        }
    }
}

// as found here: http://blog.blueboxes.co.uk/2009/07/21/rendering-xaml-to-a-jpeg-using-silverlight-3/
// also see attribution to SO post here: http://stackoverflow.com/questions/1139200/using-fjcore-to-encode-silverlight-writeablebitmap
private static void SaveBitmapToJpeg(WriteableBitmap bitmap, Stream fs)
{
    //Convert the Image to pass into FJCore
    int width = bitmap.PixelWidth;
    int height = bitmap.PixelHeight;
    int bands = 3;
    byte[][,] raster = new byte[bands][,];
    for (int i = 0; i < bands; i++)
    {
        raster[i] = new byte[width, height];
    }
    for (int row = 0; row < height; row++)
    {
        for (int column = 0; column < width; column++)
        {
            int pixel = bitmap.Pixels[width * row + column];
            raster[0][column, row] = (byte)(pixel >> 16);
            raster[1][column, row] = (byte)(pixel >> 8);
            raster[2][column, row] = (byte)pixel;
        }
    }
    ColorModel model = new ColorModel { colorspace = ColorSpace.RGB };
    FluxJpeg.Core.Image img = new FluxJpeg.Core.Image(model, raster);
    //Encode the Image as a JPEG
    MemoryStream stream = new MemoryStream();
    FluxJpeg.Core.Encoder.JpegEncoder encoder = new FluxJpeg.Core.Encoder.JpegEncoder(img, 100, stream);
    encoder.Encode();
    //Move back to the start of the stream
    stream.Seek(0, SeekOrigin.Begin);
    //Get the Bytes and write them to the stream
    byte[] binaryData = new Byte[stream.Length];
    long bytesRead = stream.Read(binaryData, 0, (int)stream.Length);
    fs.Write(binaryData, 0, binaryData.Length);
}

private static Stream GetLocalFilestreamFromFileDialog(string defaultExtension)
{
    // save to user-specified location (requires user interaction)
    var dialog = new SaveFileDialog();
    dialog.DefaultExt = defaultExtension;
    dialog.Filter = dialog.DefaultExt + " File|*" + dialog.DefaultExt + "|All Files|*.*";
    if (dialog.ShowDialog() == true)
    {
        return dialog.OpenFile();
    }
    return null;
}
private static Stream GetFileStreamFromIsolatedStorage(string filename, FileMode fileMode)
{
    // save to IsolatedStorage with no user interaction
    var userstore = IsolatedStorageFile.GetUserStoreForApplication();
    var locations = userstore.GetDirectoryNames();
    return new IsolatedStorageFileStream(filename, fileMode,
        IsolatedStorageFile.GetUserStoreForApplication());
}