using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

namespace Base64Study
{
    /// <summary>
    /// base64编码在传统.net程序中的应用(by 菩提树下的杨过 http://yjmyzz.cnblogs.com/)
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {

string imgstring = GetBase64FromFile("c:\\self.png");
            Console.WriteLine(imgstring);

Bitmap bitmap = GetImageFromBase64(imgstring);
            bitmap.Save("c:\\self2.png", ImageFormat.Png);

Console.Read();
        
           
        }

/// <summary>
        /// 将文件转换为base64字符串
        /// </summary>
        /// <param name="filePath"></param>
        /// <returns></returns>
        static string GetBase64FromFile(string filePath)         
        {
            byte[] b = File.ReadAllBytes(filePath);
            return Convert.ToBase64String(b);
        }

/// <summary>
        /// 从base64字符串还原图片
        /// </summary>
        /// <param name="base64string"></param>
        /// <returns></returns>
        static Bitmap GetImageFromBase64(string base64string) 
        {
            byte[] b = Convert.FromBase64String(base64string);
            MemoryStream ms = new MemoryStream(b);
            Bitmap bitmap = new Bitmap(ms);
            return bitmap;
        }
    }
}

<UserControl x:Class="SLBase64.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    mc:Ignorable="d" d:DesignWidth="640" d:DesignHeight="480">
  <StackPanel x:Name="LayoutRoot">
        <Image  x:Name="img" Height="100" Stretch="Uniform" Source="img/self.png"></Image>
        <Button x:Name="btnToBase64" Content="转为base64字符串" Width="200" Margin="0,3,0,0"  Click="btnToBase64_Click"></Button>
        <TextBox Text="" x:Name="txtBase64" TextWrapping="Wrap" Height="150" Margin="0,3" VerticalScrollBarVisibility="Auto"></TextBox>
        <Button x:Name="btnToImg" Content="将上述base64字符串还原为图片" Width="200" Margin="0,0,0,3" Click="btnToImg_Click"></Button>
        <Image  x:Name="img2" Height="100" Stretch="Uniform"></Image>
    </StackPanel>
</UserControl>

using System;
using System.IO;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media.Imaging;
using FluxJpeg.Core;
using FluxJpeg.Core.Encoder;

namespace SLBase64
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }

/// <summary>
        /// 老外写的方法：将WriteableBitmap转化为base64位字符串
        /// </summary>
        /// <param name="bitmap"></param>
        /// <returns></returns>
        private string GetBase64Image(WriteableBitmap bitmap)
        {
            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);
            MemoryStream stream = new MemoryStream();
            JpegEncoder encoder = new JpegEncoder(img, 100, stream);
            encoder.Encode();

stream.Seek(0, SeekOrigin.Begin);
            byte[] binaryData = new Byte[stream.Length];
            long bytesRead = stream.Read(binaryData, 0, (int)stream.Length);

string base64String =
                    System.Convert.ToBase64String(binaryData,
                                                  0,
                                                  binaryData.Length);

return base64String;

}

private void btnToBase64_Click(object sender, RoutedEventArgs e)
        {
            WriteableBitmap wb = new WriteableBitmap(img, null);
            txtBase64.Text = "";
            txtBase64.Text = GetBase64Image(wb);
        }

private void btnToImg_Click(object sender, RoutedEventArgs e)
        {
            if (txtBase64.Text == "") { return; }
            try
            {
                img2.Source = null;

byte[] b = Convert.FromBase64String(txtBase64.Text);
                MemoryStream ms = new MemoryStream(b);
                BitmapImage bitImage = new BitmapImage();
                bitImage.SetSource(ms);

img2.Source = bitImage;
            }
            catch (Exception ex) { MessageBox.Show(ex.Message.ToString()); }
        }
    }
}