即使大图像，加载的缩略图也不会旋转

img = Image.FromFile(file_path);

int img_w = img.Width;
int img_h = img.Height;

int desired_size = 150;

int img_h1 = desired_size;
double resize = (double)img_h / (double)img_w;
resize = (double)desired_size * resize;
img_h1 = (int)resize;

thumb = img.GetThumbnailImage(desired_size, img_h1, null, IntPtr.Zero);