In order to generate the thumbnails of the pictures that users have uploaded in our applications, we can use the method below:

public void SaveThumbnail(string path,string thumbnailPath,int newWidth,int newHeight)
        {
            System.Drawing.Image i = System.Drawing.Image.FromFile(path);
            System.Drawing.Image thumbnail = new System.Drawing.Bitmap(newWidth, newHeight);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(thumbnail);
            g.DrawImage(i, 0, 0, newWidth, newHeight);
            thumbnail.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
        }