var handle = bmp.GetHicon();  //得到圖標(biāo)句柄
return Icon.FromHandle(handle); //通過句柄得到圖標(biāo)

/// <summary>
/// 轉(zhuǎn)換Image為Icon
/// </summary>
/// <param name="image">要轉(zhuǎn)換為圖標(biāo)的Image對象</param>
/// <param name="nullTonull">當(dāng)image為null時是否返回null。false則拋空引用異常</param>
/// <exception cref="ArgumentNullException" />
public static Icon ConvertToIcon(Image image, bool nullTonull = false)
{
  if (image == null)
  {
    if (nullTonull) { return null; }
    throw new ArgumentNullException("image");
  }

  using (MemoryStream msImg = new MemoryStream()
           , msIco = new MemoryStream())
  {
    image.Save(msImg, ImageFormat.Png);

    using (var bin = new BinaryWriter(msIco))
    {
      //寫圖標(biāo)頭部
      bin.Write((short)0);      //0-1保留
      bin.Write((short)1);      //2-3文件類型。1=圖標(biāo), 2=光標(biāo)
      bin.Write((short)1);      //4-5圖像數(shù)量（圖標(biāo)可以包含多個圖像）

      bin.Write((byte)image.Width); //6圖標(biāo)寬度
      bin.Write((byte)image.Height); //7圖標(biāo)高度
      bin.Write((byte)0);      //8顏色數(shù)（若像素位深>=8，填0。這是顯然的，達(dá)到8bpp的顏色數(shù)最少是256，byte不夠表示）
      bin.Write((byte)0);      //9保留。必須為0
      bin.Write((short)0);      //10-11調(diào)色板
      bin.Write((short)32);     //12-13位深
      bin.Write((int)msImg.Length); //14-17位圖數(shù)據(jù)大小
      bin.Write(22);         //18-21位圖數(shù)據(jù)起始字節(jié)

      //寫圖像數(shù)據(jù)
      bin.Write(msImg.ToArray());

      bin.Flush();
      bin.Seek(0, SeekOrigin.Begin);
      return new Icon(msIco);
    }
  }
}