重要代码：

Bitmap bm = new Bitmap(origin);
            bm.MakeTransparent();

string Name_ = "C:\\Users\\xx\\Downloads\\download\\" + DateTime.Now.Ticks.ToString() + ".ico";Size size = new Size(256, 64);ConvertImageToIcon(@"C:\Users\xx\Desktop\orgin.jpg", Name_, size);/// <summary>/// 图片转换为ico文件/// </summary>/// <param name="origin">原图片路径</param>/// <param name="destination">输出ico文件路径</param>/// <param name="iconSize">输出ico图标尺寸，不可大于255x255</param>/// <returns>是否转换成功</returns>public static bool ConvertImageToIcon(string origin, string destination, Size iconSize){Bitmap bm = new Bitmap(origin);bm.MakeTransparent();Image image = new Bitmap(bm, iconSize); //先读取已有的图片为bitmap，并缩放至设定大小//Image image = new Bitmap(new Bitmap(origin), iconSize); //先读取已有的图片为bitmap，并缩放至设定大小MemoryStream bitMapStream = new MemoryStream(); //存原图的内存流MemoryStream iconStream = new MemoryStream(); //存图标的内存流image.Save(bitMapStream, ImageFormat.Png); //将原图读取为png格式并存入原图内存流BinaryWriter iconWriter = new BinaryWriter(iconStream); //新建二进制写入器以写入目标图标内存流/*** 下面是根据原图信息，进行文件头写入*/iconWriter.Write((short)0);iconWriter.Write((short)1);iconWriter.Write((short)1);iconWriter.Write((byte)image.Width);iconWriter.Write((byte)image.Height);iconWriter.Write((short)0);iconWriter.Write((short)0);iconWriter.Write((short)32);iconWriter.Write((int)bitMapStream.Length);iconWriter.Write(22);//写入图像体至目标图标内存流iconWriter.Write(bitMapStream.ToArray());//保存流，并将流指针定位至头部以Icon对象进行读取输出为文件iconWriter.Flush();iconWriter.Seek(0, SeekOrigin.Begin);Stream iconFileStream = new FileStream(destination, FileMode.Create);Icon icon = new Icon(iconStream);icon.Save(iconFileStream); //储存图像/*** 下面开始释放资源*/iconFileStream.Close();iconWriter.Close();iconStream.Close();bitMapStream.Close();icon.Dispose();image.Dispose();return File.Exists(destination);}