[StructLayout(LayoutKind.Sequential)]
        public struct SHFILEINFO
        {
            public IntPtr hIcon;
            public IntPtr iIcon;
            public uint dwAttributes;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public string szDisplayName;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
            public string szTypeName;
        };
        class Win32
        {
            public const uint SHGFI_ICON = 0x100;
            public const uint SHGFI_LARGEICON = 0x0; // 'Large icon
            public const uint SHGFI_SMALLICON = 0x1; // 'Small icon
            [DllImport("shell32.dll")]
            public static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);
            [DllImport("shell32.dll")]
            public static extern uint ExtractIconEx(string lpszFile, int nIconIndex, int[] phiconLarge, int[] phiconSmall, uint nIcons);
        }
        private void button1_Click(object sender, EventArgs e)
        {
            openFileDialog1.ShowDialog();
            SHFILEINFO shinfo = new SHFILEINFO();
            Win32.SHGetFileInfo(openFileDialog1.FileName, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), Win32.SHGFI_ICON | Win32.SHGFI_SMALLICON);
            Icon myIcon = Icon.FromHandle(shinfo.hIcon);
            FileStream fileStream = new FileStream("E:\\1.ico", FileMode.Create);
            myIcon.Save(fileStream);
            fileStream.Close();
        }