仅降低图像质量时为什么旋转图像？

Question

我已经按照这个post的答案来减小上传的图片大小。图像尺寸减小了，但它也旋转了图像本身（不应旋转）。

我看不到代码的任何部分都在旋转图像，也不知道代码在做什么。

因此，我希望可以进一步解释代码的作用以及仅降低质量时为何旋转图像。

为方便起见，我在此处复制了post答案

// Make sure to include this at the top
   using System.Drawing.Imaging;


/// <summary> 
/// Saves an image as a jpeg image, with the given quality 
/// </summary> 
/// <param name="path"> Path to which the image would be saved. </param> 
/// <param name="quality"> An integer from 0 to 100, with 100 being the highest quality. </param> 
    public static void SaveJpeg (string path, Image img, int quality) 
    { 
        if (quality<0  ||  quality>100) 
        throw new ArgumentOutOfRangeException("quality must be between 0 and 100."); 

        // Encoder parameter for image quality 
        EncoderParameter qualityParam = new EncoderParameter(Encoder.Quality, quality); 
       // JPEG image codec 
       ImageCodecInfo jpegCodec = GetEncoderInfo("image/jpeg"); 
       EncoderParameters encoderParams = new EncoderParameters(1); 
       encoderParams.Param[0] = qualityParam; 
       img.Save(path, jpegCodec, encoderParams); 
    } 

/// <summary> 
/// Returns the image codec with the given mime type 
/// </summary> 
    private static ImageCodecInfo GetEncoderInfo(string mimeType) 
    { 
        // Get image codecs for all image formats 
        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders(); 

        // Find the correct image codec 
        for(int i=0; i<codecs.Length; i++) 
           if(codecs[i].MimeType == mimeType) 
               return codecs[i]; 

         return null; 
     }