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; 
 }