Image myImage = SaveJpeg(destImagePath, myImage, 50);

// add this!
using System.Drawing.Imaging;    
    //  Saves an image as a jpeg image, with the given quality     
    //  Gets:    
    //    path   - Path to which the image would be saved.    
    //    quality - An integer from 0 to 100, with 100 being the     
    //            highest quality    
    public static void SaveJpeg(string path, Image img, long 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);
    }
    
    //  Returns the image codec with the given mime type
    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 - 1)); i++)
        {
            if ((codecs[i].MimeType == mimeType)) 
            {
                return codecs[i];
            }
        }
        return null;
    }

using System.Drawing  .NET Classes used :

private void SaveThumbNail (string folder, string filename)
{
	System.Drawing.Image image = System.Drawing.Image.FromFile(folder + filename);
	System.Drawing.Image thumbnailImage = image.GetThumbnailImage(250, 250,  new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero);
	string thumbnailPath = folder + "\Thumbnail.JPG";
	thumbnailImage.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
}

///  <summary>
/// Required, but not used
/// </summary>
/// <returns>true</returns>
public bool ThumbnailCallback()
{
	return true;
}