Thanks Eric! works great.
I changed a little bit.
Only reply for someone who needs to make it relative to site:
thumb.Save("c:\\temp\\1" + args.FileName, System.Drawing.Imaging.ImageFormat.Png);
changed to
string dir = Context.Server.MapPath("~/Files/th/");
thumb.Save(dir+args.FileName, System.Drawing.Imaging.ImageFormat.Png);
Thanks!