//Get an image from file
    Image image = Image.FromFile("D:\\test.jpg");
    Bitmap bitmap = new Bitmap("D:\\test.jpg");

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Text;

namespace NetUtilityLib
{
  public static class ImageHelper
  {
    /// <summary>
    /// Convert Image to Byte[]
    /// </summary>
    /// <param name="image"></param>
    /// <returns></returns>
    public static byte[] ImageToBytes(Image image)
    {
      ImageFormat format = image.RawFormat;
      using (MemoryStream ms = new MemoryStream())
      {
        if (format.Equals(ImageFormat.Jpeg))
        {
          image.Save(ms, ImageFormat.Jpeg);
        }
        else if (format.Equals(ImageFormat.Png))
        {
          image.Save(ms, ImageFormat.Png);
        }
        else if (format.Equals(ImageFormat.Bmp))
        {
          image.Save(ms, ImageFormat.Bmp);
        }
        else if (format.Equals(ImageFormat.Gif))
        {
          image.Save(ms, ImageFormat.Gif);
        }
        else if (format.Equals(ImageFormat.Icon))
        {
          image.Save(ms, ImageFormat.Icon);
        }
        byte[] buffer = new byte[ms.Length];
        //Image.Save()會改變MemoryStream的Position，需要重新Seek到Begin
        ms.Seek(0, SeekOrigin.Begin);
        ms.Read(buffer, 0, buffer.Length);
        return buffer;
      }
    }

    /// <summary>
    /// Convert Byte[] to Image
    /// </summary>
    /// <param name="buffer"></param>
    /// <returns></returns>
    public static Image BytesToImage(byte[] buffer)
    {
      MemoryStream ms = new MemoryStream(buffer);
      Image image = System.Drawing.Image.FromStream(ms);
      return image;
    }

    /// <summary>
    /// Convert Byte[] to a picture and Store it in file
    /// </summary>
    /// <param name="fileName"></param>
    /// <param name="buffer"></param>
    /// <returns></returns>
    public static string CreateImageFromBytes(string fileName, byte[] buffer)
    {
      string file = fileName;
      Image image = BytesToImage(buffer);
      ImageFormat format = image.RawFormat;
      if (format.Equals(ImageFormat.Jpeg))
      {
        file += ".jpeg";
      }
      else if (format.Equals(ImageFormat.Png))
      {
        file += ".png";
      }
      else if (format.Equals(ImageFormat.Bmp))
      {
        file += ".bmp";
      }
      else if (format.Equals(ImageFormat.Gif))
      {
        file += ".gif";
      }
      else if (format.Equals(ImageFormat.Icon))
      {
        file += ".icon";
      }
      System.IO.FileInfo info = new System.IO.FileInfo(file);
      System.IO.Directory.CreateDirectory(info.Directory.FullName);
      File.WriteAllBytes(file, buffer);
      return file;
    }
  }
}