So you have an image saved to your database as a byte array, below is a neat little method that accepts it as a parameter, converts it to a thumbnail and spit it back out as a byte array.
public static byte[] MakeThumbnail(byte[] myImage, int thumbWidth, int thumbHeight) { using (MemoryStream ms = new MemoryStream()) using (Image thumbnail = Image.FromStream(new MemoryStream(myImage)).GetThumbnailImage(thumbWidth, thumbHeight, null, new IntPtr())) { thumbnail.Save(ms, System.Drawing.Imaging.ImageFormat.Png); return ms.ToArray(); } }